I made some gp/fondant mix flowers to put on some cupcakes swirled with bc. The flowers got soft and didn't hold up. Any way to prevent this? I have a bc cake to do this weekend with hydrangea flowers made of GP.

They shouldn't have softened up unless they were in a closed container. The only time I've ever had trouble with gumpaste softening on a cake was when I put it in one of those tupperware cake carriers, and the moisture in the icing recirculated and was absorbed into the gumpaste.

If you're really worried about it, just put the flowers on at the last minute so that they're on the cake for as short a time as possible.