Dremel is way too fast and too small - you're going to gouge the plastic.
Even if you manage to slow it down, it's going to take a long time to do the whole lens.
What I did was get a buffer attachment for a drill.
Most of the buffer covers - usually wool or equivalent - are too course for your application.
I used a discarded T-shirt and covered the whole thing - cut & tied to fit snugly - to give you a more finer (smoother?) buffing surface.
Work slowly until you get a feel for the buffing action.
-Ted