I havent done that, but I think you must try to put the quantization at the low end I mean at 1/32, and try to step recording your rhythim at half the tempo, so when you put the tempo you´ll have to doble it.

So If you´re trying to record a 100 tempo loop, of 1 step, you can make 2 steps at 50 tempo so the lowest quantization can bring you the best possible flam effect.

Give it a try.