Moongel actually works just fine on cymbals. For a ride, put it on the far side from you, out toward the edge. The further out, the less wash.
Another trick is to get really large felts. That can tame a ride a bit.
If you don't like that, try to find some gaffers tape. It looks like duct tape but is made not to leave residue. I really get upset if I see someone helping and putting duct tape over my cables. You just can't get the goo off.
But any tape, blue painters, gaff, or anything else, will eventually leave a residue if it's left on long enough.
To more directly answer the OP, about a 2" by 3" piece of gaff tape on the bottom will damp the wash of a ride cymbal. If you put it under the area where you hit, you'll get a duller, clangier sound. Putting it on the far side will let the stick sound be more natural but have less wash. The further out toward the edge you put it, the deader you'll make the cymbal. Since gaff tape comes right off, it's easy to experiment. But if you're really trying to kill a washy cymbal, I'd start with 2/3's out.
I have three ride cymbals. A K Custom Dry, a regular K med, and a Dream Bliss (which is really washy). I looked all over for the K Dry to find one that pinged instead of clanged, having gone though several ping rides and various others. But after playing that ride for about 5 years, I just sold it to a buddy (who'd had a really dry 60's A stolen). I can dry up the regular K with moongel if I need to when recording. Other than that, I've discovered that a bit of wash or shimmer helps fill out the ride sound. Usually folks switch from the hats to the ride when you want to kick up the energy and dynamics. But a really dry ride falls down after washing the hats as the song picks up.