if you have an applique pressing sheet (or some left over release paper from some fusable) you can lay your product fusable side down on the pressing sheet, then using a medium heat iron press the backing to the fusable- let it cool completely then peel off the pressing sheet. i *would not use wax paper* it would put a waxy residue on the fusable and chances are the fusable would no longer adhere.
i often keep sheets of (release paper) after using a fusable- if i didn't cut out shapes and have a fairly large piece- i just fold it up & put it aside-so if i need it i have it- sometimes fusables just *let loose* of their release paper & i might have to fix it- but if i don't have any handy i've used my applique pressing sheet many times- just make sure you let it cool, then carefully lift/peel the fusable and it's paper back off the sheet