I think about it more as keeping the quilt on my chest than in my lap. I tried throwing it over my shoulder but I couldn't quite get it through feel comfortable.
I also got a couple of cheap adjustable tables and put those on either side of me to help hold the quilt. I put Artbin Super Satchel boxes, books, and the extension table for my old machine around my extension table to make a bigger surface as well.
I am attaching a photo of me quilting a queen-sized quilt on my Janome MC6700p. It was heavy to get everything situated, but once I had it set up so the front was folded up on my chest and the sides could move freely (with the occasional shove through the throat on the right) it chugged right along.