The wrong technique, but it works for me....
 

I hold one end of course, and the other is on the edge of the painting. Well, actually the end of the dowel is past the edge of the painting, so only the side of it is touching the edge. Other than once, when I wasn't used to it and it slipped, it has worked for me. This "dowel only" is due to my laziness (and cheapness, I suppose) - I got a wooden bead for the end and was going to drill it to fit, and got some leather to tie around it, and was fully intending to make it the right way....but never got around to it.

I've been using the EZ Rest which is a mahl stick sort of thing that clamps onto your easel and pivots around to wherever you want it.... Since it's attached you don't need to hold it with your free hand. It's maybe a little further out from the canvas than I'd have prefered at first, but I've gotten used to it and feel lost without it now.

I also use a cane when I'm painting on my travel easel, but am much less comfortable with it.

For those who use a wooden dowl -- I stuck a tennis ball at the end of my dowl. It's lightweight and the roughness of the ball grips the edge of the canvas.