Again, not an expert of any sort, but in case it's of any help - I am in a similar situation with Bonnie, who is a last year's hatch and has never been broody before - but she is currently sitting, has been for over a week... I hope that she stays, and I plan to put in 20+ eggs in the incubator on Friday... here's my plan:
 
-give Bonnie a few eggs of her own (instead of the golf ball she is currently trying to hatch, lol) at the same time - I think she is more likely to stay after they start developing, or at least I think they feel it
 
-set up a brooder with the heat lamp next door to Bonnie's "apartment" (not sure if you have seen my setup, it's basically 3 separate enclosures next to each other, I can repost the photo if you want
 
-provided Bonnie stays (not much to do there but hope and pray), do a test with a couple of bator chickies first - if all works out, bring in the rest of them
 
-if she takes them on but can't cover them, remove the "wall" between "apartments" - it would basically become double the space, and chickies could warm up under the heat lamp if needed, or move away from it if not cold... it's getting very warm here, so this would only be needed for a very short time initially, and then only at night for a few weeks
 
-if she doesn't take them on, go with plan B and keep them separate (though still next door) - watch like a hawk the first couple of days (should be the weekend) and, if she is mean to the bator chicks, separate the outdoor area as well. I really doubt it will come to this though, she has a sweet chickenality, even while broody (i.e. she doesn't try to take off my hand when I lift her/bring her food, etc.)
 
I don't know what your setup is, but hopefully my plan sparks some ideas for you as well... I do advise to be ready with a brooder all set up just in case, because yeah, that is a lot of chicks.