Not familiar with this specific printer, but if it offers a white ink, you can try printing a process gold and then apply a foil film for plastisol inks overtop. I did this for a sample in my shop and it seemed to hold up. The process gold will fill in in the event the film wears away or doesn't attach to the entirety of the design (fairly common with those films I've read).
Given that it's a customer supplied item though, I would turn them away unless they have plenty for you to do and don't mind you experimenting with their product.
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