I know Jim Lee has a nose ring sander and I highly recommend it!

But, if you are in a bind and need one quick, you can make one from two pieces of 1/8th ply and a scroll saw.

I make a square about 2 1/2" wide for a 2" nose.  I mark across it from corner to corner on the diagonal to ge the center.  I drill this to match the prop shaft on the engine.  I make another one but I cut the center out about 1" diameter.  This I face with sandpapaer and glue it (on the diagonal) to the first piece.  This leaves "handles" for your fingers to work.

Place it on the prop shaft with the sandpaper facing the nose ring (plug all the engine openings with paper towel!) and snug the prop nut on it.  Begin to turn it back and forth, round and round!  As it gets loose, tighten the nut slightly.
This set up will give you up to 1/8th" clearance from the face of the drive washer (spinner back plate) to the face of the nose ring.  Plus it is EXACTLY aligned with the drive washer so the gap around the nose is even.

EDIT:  Do get one of Jim's pieces if you can!  This is just for "emergency" use!