Q. Can water be used as a medium to propel rocks into space?
That sounds implausible to me.
Q. Can the "radiometer effect" guide asteroids into stable orbit?
The asteroid would have to already be in a stable orbit. The effects of radiation pressure are small, and would have to act over a very long time. Unless the asteroid were already in a somewhat stable orbit, it would not remain close enough to the source of radiation for there to be much effect.