I tried this years ago and decided it wasn't a good idea. My reasoning was that it would be like vermiculite/pearlite. The stuff is so light it just blows away in the least draught, it doesn't hold water and goes just as green as the damp soil very quickly. Then you still have to dispose of it when you've finnished, it won't degrade in the compost and if you throw it on your garden and birds pick it up it can kill them. If you have damping of problems with your seedlings, try less water and water from underneath to keep the top layer of compost dry. Just my view, though. :)