Just make sure you have holes along the side of the cup for water flow.In true forum user fashion I asked the question first then did the research. I saw both of these as well as a few instances of people saying to sew it onto a pice of rubble (pierce the foot with a needle/thread, legit sew it on) but knowing how big a PITA mushroom can be I'm not sure how effective that is.
I have a bunch of seedling cups from my planted tank that I can put it in with some rubble and then mesh over the top. Hopefully that'll work.