Will this work as an incubator for 1 late egg?

Because of this fabulous heat wave, the fact our last broody and her one chick leave the nest daily hasn't been an issue.  I've been keeping tabs on her last egg and it's developing nicely.  I suspect it's only got 3 or 4 more days to go. 

However, the heat is *supposed* to break later tonight, so I'll need something for tomorrow in terms of a quickie incubator.  (Broody sits on egg all night, then leaves for the duration of the day with the chick - she guards her nest, but hasn't sat on it since chick was mobile).  As we've not purchased one, I'm trying to figure out what I could do that's on hand.  I'm not interested in hatching out bunches of chicks, so purchasing a unit seems financially wasteful.

I had a strange idea.....and wondered if this would work....

Could I use our cookie-tin water heater and use that as the 'base' for an impromtu incubator?  (The link for the water heater is here: http://www.backyardchickens.com/t/107951/cookie-tin-water-heater )

Using a strip of aluminum foil to block the egg from directly touching the lightbulb.  Perhaps putting the egg in a plastic cup and adding a second cup with a small amount of water in it (tablespoon or two).  Adding appropriate temperature/humidity guages.  Heck, I could cut out the lid and put a scrap of plexi for a 'window'.

Would this work for a 3-day need?  Would I boil our chick? 

Thank you for any input.  I really wish to see this little one survive, as nature has worked so hard to make sure she does!  (Hoping it's a she after all this effort - mental and physical!)

I thought some photos might be helpful in determining what I can do better or different or for others in the same situation.

I'm using a 7.5watt nightlight bulb inside our 'cookie tin water heater'.  When it's a water heater, it held a 25watt bulb.  Worked great at that application, so I'm trying this out as it's on hand.  The cookie tin is in the kitchen, so I'm constantly checking on it!  Thus far, so good - keeping a good temperature overall and chick seems ok during candling.

and inside is the 'good stuff', just as in the egg! 

I put "Victoria" in a aluminum-foil cup to stabilize the egg from shifting inside the improvised bator.  Next to the bulb is a small ceramic of water to boost humidity.  Thus far, it's keeping good temps/humidity as far as I can tell.  After all, this egg has been left on it's own in 115 degree heat (ok, the egg was in the shade, but still, whoa, it was hot!).  If I get a successful hatch out of this, I'll be simply blown away by what God does!

"Victoria" gets taken back to her nest every night to sleep with her Mom and sibling.  I've got a dud egg in the nest during the day, and add this one when they tuck in at night.  Seems like a huge amount of effort for the last egg out of 9, but I've GOT to give it a chance!  Mom had to take chick out, and this little one was left behind.  As it's almost 2wks behind older sibling, I'm thinking somehow the eggs got mixed up and one was left in this nest that should not have been there. 

Input and respectful criticism is welcomed.  That's how we all learn! 

This was working SO WELL! 

Egg stayed in the 'bator' during the daytime, went outside under Mom at night.  She kept it warm and snuggly through the nightfall, and in the morning, she and her chick went off to forage all day and the egg was fine with me.  Chick growing well.  Candling revealed a healthy little chick.  Went on this way for 9 days. 

Bum-bum-bum-bUMMMMMMM.....

Then, a skunk visited our homestead.  Not unusal.  But with this drought, some of the wilder critters have discovered our water out in the pens.  I guess a skunk found it's way there two nights ago.  When I walked outside in the early morning, I could smell skunk just about everywhere.  All around the pond, by the barn, by the compost bins, around the coop/pen area - no sign it actually went into the pen (I think it drank from the pond, as the stench there was horrific).  And my skittish Black Java Mom was hovering over her chick in the far back corner of their clamshell doghouse brooder house.  She had been off the egg for at least two, maybe more hours.  The egg was frigid cold.

I dashed it indoors, warmed up the heating pad, started warming the egg up on the heat pad while the incubator got warmed up.  Candled.  No movement.  Nothing.  Incubator was up to temp, put egg in incubator, left it for a couple hours.  Still, no movement.  After watching it all day, I determined the chick was most likely gone.  Got brave.  Cracked it open to discover yes, the chick was gone.  Was at least 12 days old.  Which means it was a lot younger than I thought it was! 

It's really hard, but the lesson here is yes, this system did work as a temporary incubator.  Granted, it tood a fair amount of effort on my part to make sure egg was in the 'sweet' spot.  Had to learn where exactly that was.  But, yes, this did work.