Hm. Couldn't you have a mirror that's only reflective on one side? I suppose it would be heavier...

If the sunward side is black, it will suck up visible EMR and re-emit it as heat.

The stealthiest way I thought of to move stuff is vie passive flybys but there you need to go near planets so sensors near planets will pick you up. You could try rotating tethers but they tend to have at least one large dimension and will limit you to a few km/s, probably.