Funny you should ask ... I was reading two books on thread work (thread painting and other detail work) and both mentioned using hoops in the machine to stabilize the fabric and thought ... huh?
Then I went to Paducah and on Sharon Schambers booth, she was there quilting away on muslin with no markings and she was using hoops to stablize!! They were called "Quilt Halo's" and she had four of them stacked together.
The neat thing about these is that you don't put the quilt "in" them like an embroidery hoop - you just place the hoop over the quilt and around the needle (the hoops are something like 8" round) so it's easy to pick them up and keep moving around the quilt.
Here's a link to her site where she sells them.
http://www.sharonschamber.com/shoppi...ewproducts.htm
I've also seen embroidery type hoops where you insert the quilt inside two concentric hoops and clamp them together - but these are flatter for machine work. Don't remember where I saw them, perhaps in one of the books I was reading.