For gluing fretwork to a backer board, I like to use the thick type of CA glue. I apply the glue to the back of the fretwork before gluing the two together. I have tips that attach to the glue applicator, the tips have a needle point which is great for those small little pieces that are so delicate. Even with just the glue applicator, you can apply the glue at just the spot where you need it. I did find that sometimes when I'm trying to glue the cutting to the backer board, the cutting will want to slip or slide a little because of the glue being so slippery. What I did to remedy that problem, was I took a piece of 3/4" plywood and attached pieces of wood to the sides and ends. The pieces that I attach to the plywood, are just 1/4" strips of pine that are wide enough that when you attach it, it will be about 1/4"-3/8" above the surface of the plywood. So, when I go to apply the cutting to the backer board, all I do is just lay the backer board in place on the plywood with the face in the up direction, I then apply the glue to the cutting and just lay it in on top of the backer board. It's very easy to place the cutting in it's proper location, because those strips of wood that are higher then the 3/4" plywood hold it right where it belongs. Most of my fretwork is all done on the same size piece of wood, that is why my jig works so well. Just in case of glue squeeze out on the sides or ends, I usually will have a piece of saran wrap or waxed paper placed so that the glue can't come in contact with the wood that the jig is made out of. Once the cutting is in its place, I lay another piece of plywood on the top of the cutting with a gallon of paint on top of it used to weigh the cutting down.
Len