the spring factory I work for makes a clay pigeon holder called UNCLE MARVS STILL TARGET HOLDER. basicly it's a heavy piece of wire formed to hold a clay pigeon and will sit anywhere. they sell 3 for $14.00 at www.allaboutshooting.com
I'm not sure if they have ever sold any or not but I think they got endorsed by the NWTF.

I got mine free!