I've never done it, but have been thinking about it for years now. Today on my ride to work I rode past at least 5 Cacti completely full of prickly pears. I think you would be on the right track to use them in a Heff, or a wheat beer of sorts, the tart acidity of the fruit would be good with them. Or a wise style sour beer would be excellent too.
I might have to raid some of these Cacti and get a few lbs for a pure, and freeze it for later. too many beers in the pipeline for me, but I'd like to hear about your experiences with them if you try some thing.