I used an X-acto knife and regular masking tape. It has to be very light pressure, though, to prevent scratching the lenses. I like your idea about the vinyl, though! Makes it easy to repeat the mod (if someone else wanted you to do it for them).

It takes me a while to do a set (and I've been doing a BUNCH since I started posting these pictures) because of the masking. The rest of the process takes literally minutes. I just got done with a set of lenses for one guy who wanted tribal-type symbols instead of the open ovals I did. I had to match his tatoo. The other cool one I did was for a '01 Lightning using Lightning bolts instead of the ovals. Turned out good. The possibilities are endless.

Thanks for the cool tip!