I've wondered about this for some time; a racer friend of mine, among other sources, convinced me to try tubeless on my mtn. bike. I bought a Stan's kit, with the rim strips and solution, and hooked up a set of Hutch Scorpion UST's with the Mavic 223 rims. The system worked perfectly, and I immediately noticed the increased performance. When the Scorps wore out, I got a smokin' deal on some non-UST Spiders, some 200g lighter and a sweet tread pattern. But no matter what we both did, the Spiders wouldn't seal up. So I installed tubes, and ran it that way ever since.
Here's the trick; during our efforts to air up the Spiders, my bud told me about the non-UST Mythos tires he was running, and how they needed about half a bottle of Stan's to seal the porous sidewalls. I had the brainstorm of sealing the sidewalls with regular fix-a-flat. Since the deal I got on the Spiders was a bulk purchase, I had other tires -- all of which were sealed up with the fix-a-flat. I have since noticed that the f-a-f treatment reduces tube friction inside the standard tire, too.
Last week, my bud got a new set of Mythos for his bike, and decided to try the f-a-f in one tire vs. the Stan's in the other. He wound up doing both tires with the f-a-f! He tells me it's twice as messy to set up, but it works perfectly!
Has anyone else thought of this, or tried it? Anyone else willing to try it? I'm likely to, when my next tire change rolls around.