One other note. Alesis equipment works best with Reflection plates or off set trigger mounting (ie. Ddrum red shots or the L bracket style triggering).
Well, I didn't have all the foam necessary around the house, while I did have the parts on hand for an L-bracket style attempt, so that's what I went for.
It works amazingly well, especially if I treat it as a single zone. I mounted a plastic L-bracket I found in my junk drawer, a block of foam on top of that, a piezo on top of that, and half a nerf ball (the kind that some nerf guns shoot) on top of the piezo, reaching about 1/8" over the rim, touching the homemade mesh head. I also put a piezo on the drum shell for a rim trigger.
There's quite a bit of crosstalk between the head and the rim trigger. Not sure if the foam supporting the piezo from below transmits vibration too well (it's rather rigid), or if I need to adjust my D4's setting better. And it is rather hot where the ball touches the head, but I can avoid that.
All in all, I'm quite happy with it! I tried to post a picture here, but I couldn't get it to work.
Thanks for your help! (Here, and in this forum on other topics, and on other forums as well!)