What about something like this:
Maybe not this item specifically, but if you could get the toggle through the rubber mount inside there, and then stop the screw against the end of the chassis tube (with a washer or something), then as you tighten the screw, it should pull it out. Or just grab the screw with a pair of vice grips and yank like crazy. If you had a way to attach a slide hammer, that would be even better. If you could use a needle or something to get some lube between the chassis tube and the rubber mount, that may help. PB Blaster also may penetrate around the sides and loosen everything up. Can you bore it out with increasing drill bit sizes?
I’m just throwing suggestions out there to get the wheels turning. It’s rubber, and you can defeat it with willpower and cunning.
2010 Spirit [Birel] SP32 // SRS CR125 - Stock Honda [#08]
Hill Country Kart Club - New Braunfels, Texas - http://daledaugherty.wordpress.com/