I'm thinking about doing this same thing. I have an older Cannondale road bike with a 53/36 combo up front. I find the 53 tooth ring completely useless for what I typically ride for. I can't just take it off though, as the chainring bolts are long and hold the two rings together. I would like to put a dummy ring with no teeth, maybe made out of plexiglass, in place of the 53, to help avoid any grease on the pants.