When I do Freezer paper applique I use a washable glue stick to turn the seam allowances under/over the FP.
Easy Peasy ~ IMO.
I put a piece of scrap paper (like a torn out magazine page underneath my work area and just smear a dab of glue on the SA and turn it. Sometimes I rolled/pinch with my fingers, and sometimes I use a toothpick or stiletto to smooth out the turned SA before it goes dry. I originally took a class on Invisible Machine Applique and the instructor recommended Uhu glue sticks and the above method.
I tried the starch method, but just preferred the glue stick. Hope you find a method you like. =)
Good Luck!!
Donna MC