Well...there are several problems to your theory. First and foremost, if these eggs were sold for eating, they should have been refrigerated. This doesn't ALWAYS kill the embryo, but it certainly wouldn't help your cause. Second, no farmer that is selling eggs for a profit is going to keep random roos running around just for fun. I know you alluded that you thought there might be "guard" roos to "protect" the hens. I doubt that is the case. I would agree that you'd have a better shot by getting fertile eggs from a farmer's market scenario than from a grocery store, but I still think it is unlikely. Also, your "incubator" doesn't sound like anything that would hatch anything, anyway. How are you controlling humidity/temp, etc? A 30W bulb in an open basket isn't going to properly heat the eggs and you will have whatever humidity is in your room (which may be OK if you are in a very humid area...but usually needs to be supplemented). Anyway, call me a killjoy, too...if you want. Just MHO. I wouldn't have wasted my time/money. It's difficult enough to get eggs you know are fertile to hatch, let alone ones that aren't supposed to be. I don't think you'll see anything hatch. Good luck.
if not I would throw them out...that way you can save some blown up messes if they rot before day 21
