Dave,
The best solution is to test running thinned wash with lacquer thinner over Future on a scrap, see if there's any reaction. Just remember to give your Future 2 or 3 days to cure up properly. I've used turps over Future with no bad results, but that's oil paint weathering. The other thing is to work very lightly with your thinners in removing the excess wash. When I remove my excess, I work an area for a little bit, move on, come back to the first spot ten or twenty minutes later, giving it a bit of time to rest in between and not work through the gloss layer.
Best to try it out on a scrap and see what works best for you.