A friend uses a fold up plastic table on risers and clamps the sandwich down at one end to hold it tight.
I use a double bed in our guest room, pinning the backing to the quilt underneath it to keep it taut and scooting a couple of old cutting mats underneath for pinning. This isn't great for the back, but I can leave it and come back later. I also quilt bigger quilts in sections so I don't have to sandwich a giant quilt all at once.