I realize I answered a post in the request forum (/me waves @ eelgoo ), but it might be useful information here. They don't have Fit Control that works on Genesis 8.1 yet, but you can still make the original Fit Control for 8.0 work.
Here is exactly what I did to bang it into place on an 8.1 dollie, using a typical bra, panty, shirt, and jeans:
1) load the 8.1 figure, and get her dressed with all the stuff I want Fit Control to work on.
2) load the 8.0 (Old Genesis 8) figure, and for each of the clothes I put on 8.1, "Fit To" the 8.0 figure ("Fit To" is in Parameters -> General -> Constraints )
3) after that, add all the Fit Control morphs to the clothes
4) once you're ready, take those clothes and “Fit To” the 8.1 figure again.
The pair of jeans that fit all wonky, but cranking up collision a couple of notches (and smoothing a notch) fixed it. The rest of the clothes (the shirt and underwear) transferred just fine and the Fit Control morphs work as advertised from a quick bit of sampling I did.