...allow UMD to be used on psionic items?
I don't think you can use it to fake pp
He could just get a Dorje of Hustle if you let him, though, and skip the tattoo stuff.
So if I understand correctly, tie a Transducer to a Capacitor to a Hustle Tattoo so that the tattoo recharges at 1 pp per day (at a cost of 1 pp to you each day) or that you can recharge it yourself at 1 pp for every 2 pp invested?
That's right. Although
anyone can use a psionic tattoo (they're the psionic equivalent of potions). I'm not sure how (or if) one with that setup would recharge on a non-psionic wearer, though.
What other ways, aside from the measily 2 pp Hidden Talent gives, are there?
He could be a Kalasthar.
Although... as a dragonborn, I'm not sure he'd keep the extra power points. He'd keep the psionic subtype, but the extra power point per CL is a racial feature...