I'd agree with Welshy,
I've actually done a similar thing before, just to experiment.
I used a non-ust tyre (furious fred) on a ZTR Olympic wheelset.
Basically I fitted the tyre, filled with some selant, spun it to get it spread evenly, then fitted a superlight maxxis tube.
It worked to a degree, i did loose a bit of air when I pinch'ed, but thats because i don't think it leaked with enough pressure to seat the tire.
Before you ask why...
It was a road&mtb event, so obviously you needed a fast lightweight tire, with enough tread to ride ST, me being a big bloke, I wasn't going to take any chances!
-Josh