I have great news for you. To repair your squeaky floors there are two products that you might want to take a look at. The first is Squeak-Relief from Accuset Tool Co. which installs from below the floor using an aluminum floor brace and the second is Squeeeek No More from O'Berry products. The latter uses the snap off screw you wrote about.
For the Squeak-Relief product line check out Accuset's web site at Squeakyfloor.com With regard to Sqeeeek No More check out the worksavers.com web site which should have both products available in about 30 days.
If you need any more info on either product contact me Jim@worksavers.com