Usually you make a bit of a nick on the down side of the branch, and weight it down with a rock or a big staple. It helps to put some good, loose dirt under it. After it seems to have some good roots, don't dig it up right away; cut it off from the parent without disturbing it and leave it for a season.

I understand you might weigh down the branch with a rock and cover with soil and pray a bit. It should root right there. Soon as it develops some roots you can sepoarate it or just let it go as is.

Thanks for the information, birdgardner and betsybr.

I've had it layer itself but basically just the way birdgardner describes. I let it overwinter attached, cut it and left it undisturbed to lessen any shock and then dug it up and gave it to my neighbor.
It has also suckered a little but the one sucker I dug up didn't have a lot of root on it. It didn't live when I gave it to a friend. I'm not sure if she left it in the pot or tried to put it right in the ground.
The blooms are heavy and will weigh down. But as the shrub gets older, it will mound on itself. As you see, it gets so many flowers, you won't see them all when it blooms. So I might try to selectively prune it this year because a few lost blooms won't matter anymore.