This is what I do as well, as a matter of fact, I do all my hand quilting hoopless..only difference is the way you hold the needle,,, no rocking, just hold it like you are hand piecing... with your thimble behind to push it through

I have done some wall hangings with out a hoop with no problems.

you can baste a piece of fabric on edges, making the project wider. This can help. Plus, some use extra cloth on edges to add to thickness when doing this. Makes sense, the runner is probably thicker than one piece of fabric.
by the way.. this does work well. Good luck with you project. I quilt by hand too.
Ellen

My hand quilting without a hoop comes out great, just make sure that the piece is tacked together very well, so that the 3 parts cannot move. I also like to do quilting using a bit bigger running stitches so that the quilting can be seen just a bit.
Take care and have a great day.