Even if you get the caps to seal, twist-off bottles are made of thinner glass and I've read reports of people having a lot more bottle bombs when trying to use them.
Not worth the risk, IMHO.
You spent good money on your ingredients, and put a lot of time and care into the beer to get it ready for bottling. Isn't it worth picking up a few 12-packs of Sam Adams to make sure you have good bottles?