Trace your lens (or an existing filter) onto thin cardboard. For every filter you want to make cut 2 cardboard circles. Cut the same size holes in the middle of the circles so you have 2 rings of cardboard and place the filter you want
Check out some of the most geeky wedding rings in the market. Double helix eing, engagement rings and some more can be listed as some of the nerdy engagement rings in town. If your partner is geeky enough, such rings can be a perfect engagement ring.