Finally I tried a spray adhesive. The right kind will stay tacky long enough to put on the Nuvo flakes, although for the two tone look that I wanted for the sunflower, you have to very careful when breathing not to get have the flakes flying around too much and getting onto the wrong part of the stenciled image.
The actual stencil itself is now gorgeous, I ought to post a picture, because the adhesive stuck to it as well and of course then the flakes themselves, so it is very glittery!
If you're going to try this, make sure that you tape down the stencil so the adhesive goes where you want it to on your card surface. Also, cover over the portion that you don't want to get sticky. Any normal sheet of paper will do. I used Frog tape so it wouldn't lift up the watercolored background. And then flake at will!
I used a variety of distress inks for the background and learned that candy apple red really creates a vivid background. I obviously need more practice when embossing letters, it looks a bit sloppy.
I made one card for my daughter's "golden" birthday when she turned 25 on the 25th, which was one of my main motivating factors for trying to master the technique of using the gold flakes on the sunflower, with the distressed ink background. I didn't master it by any means but it looks close to what I wanted.
Thanks for looking.