VAD stands for venous/vascular access device. OP, a PICC is a VAD. You'll have to be more specific in the alternative method of IV administration you're considering. Central Venous Line, such as a subclavian? Broviac? Medi-port? (I'd really hope it's not a port...)
Other things to consider:
Does he really have poor venous access, or is he just a hard stick? If he has good veins, but the roll or it takes a few attempts, I don't think the infection risk of a PICC is worth it, in my opinion.
How long will he be needing treatment 3 times per week? It's my understanding that ECT treatments begin frequently but then are spaced to once weekly, twice monthly, etc. How long until he is down to just once a week? Is a PICC really worth it for one access per week?
Does he have any other psychiatric conditions? Is he able to safely care for a PICC, or is it a risk that he will pull it out, get it wet, get it dirty, etc. Would his PICC be a safety risk if other patients were to attempt to pull on it?
One more thing: Is there a reason that the IV has to come out after each treatment? Can't you leave the IV in and either heparin lock it, or do saline or heparin flushes twice a shift to keep it patent? That way he doesn't have the big risk of infection, but doesn't need to accesses every time he gets a treatment. With appropriate care, a good IV should be able to last at least through two or three treatments. He's an inpatient for now, so it shouldn't be too hard for nurses to maintain an IV.