I use a plastic folding table and drape my quilt over it, and glue it in sections with Elmer's. As long as the area I'm gluing is nice and flat it doesn't matter if the rest is rumply. I press briefly with a warm iron as I finish each section so the glue will grab on well enough not to move as I do other sections. I do each side separately - I put batting down and glue the backing on first, let that dry an hour or so, then flip it over and repeat with the top. Then I usually let the whole thing sit overnight to be sure all glue is dry before I quilt it together.
It works amazingly well, and my knees are so much happier now that I'm not crawling around on the floor. I pretty much don't get any puckers anymore at all, which I was still getting with every other technique I tried.