Beam missing works like a charm.
However, the only problem is that my mission is in subspace, and setting the texture to be invisible (or any invalid texture), causes it to appear as black (like seeing through even the skybox). While that definitely would not be a problem under normal circumstances...the asteroid shows up quite well in the swirly-blue-white clouds of subspace

EDIT: although, setting a nav bouy, sending it VERY far away...its so small that noone will ever see it. That works wonders

Since the whole exchange is scripted anyway, it should be easy to time when a beam is supposed to hit...and I guess that works 99% of the time. Good enough.