CAG eating off the bottom of playstand tray?

I am very aware that this is a bad thing. I also know what can happen if he eats his own feces. What I need to know is- how do I keep him off the bottom tray? His playstand perch doesn't have a grate and I'm cleaning the tray several times a day to be sure he doesn't ingest something disgusting. I've been positive reinforcing when he stays on the perch but I think he gets bored after awhile and ventures off the stand. Anyone have any creative ideas on how to keep him out of the tray?