i actually can't take all the credit for this. sharon schamber shows a wetting process on the frame to "iron" the backing instead of really ironing. as the fabric dries, it shrinks into un-wrinkles. i also saw a video of her squaring up a block by stretching and shrinking by wetting in place and then pressing to true it up. both methods can be found on youtube.
so i thought HAH! there's more to this shrinking thing than meets the eye.
she uses a plain old spray bottle so i do too.