Need "case folding quickcheck"

I need to build a USet that is the set of characters that might change 
under case folding. The best I have been able to come up with so far is 
something like:

[[[:Case_Sensitive:]-[:Lowercase:]][exceptions]]

where "exceptions" is basically everything in CaseFolding.txt that 
contains the word "SMALL".

Is there a better way to do this?

Thanks,
Deborah