Sharon Schamber uses glue in her Pieclique technique (book of same name). Any chance of checking it out at a local library? She uses water based liquid glue and puts a hole in the nozzle with a thick needle instead of just snipping off the top of the applicator. This give her the control to apply thin lines of glue very precisely. I'm sure - given her sensational prizewinning results - that this works, but I just am uncomfortable with glue and fabric in most situations.
Another method is to use a solution of spray starch/water and paint it onto the seam allowance and then press. This gives a very sharp firm edge that is easier to applique by machine.
What's wrong with good old fashioned basting? I baste the edges of all my applique down because I find it gives me better control and I can always add an extra stitch here and there if something needs extra hold. It also allows for slight easing to fix any stretching of fabrics cut on the bias, and you will have quite a lot of those edges in your piece. But I do most of my applique by hand. Is hand applique out of the question?
If the pieces are not too small you could use an iron on webbing. Apply a thin strip on the back of the seam edge to be turned, peel off the backing, finger press the seam allowance, then cover with a Teflon pressing sheet and use the iron to glue the edge down. Any webbing not covered by the seam will peel off the Teflon sheet, and small areas of web could even help hold your piece in place for machine sewing - just press to them onto background.
I know some love products like Wonder-Under (Vliesofix) and I suppose you could bond the whole piece to the background. If you do that you could trim off the seam allowances and machine applique the raw edges.
Hope you find a satisfactory method.