Cut the foil into squares and print the mirrored image with the plastisol adhesive directly onto the foil, then run through the dryer quickly. They can then press the foil and adhesive in one pass. I have done this before without issue, though I still prefer the ease of printing onto the shirt instead. The foil tends to want to roll up a bit so it isnt as fast as printing onto transfer paper.
Another option would be to print the adhesive or plastisol which is close to the foil color onto transfer paper (mirrored of course) and have them press that onto the shirt first, pull off the paper, then press the foil. That should work well enough.
