morphine pumps

I'm posting this question here and to several other specialty boards in hopes to find a good answer.

I'm working on a hospice unit for the last 6 months (which I love). In the past I worked in ortho for 4 years. Anytime I experienced a pt on a morphine or dilaudid pump, they were run through either a PICC or port. I have to admit that I haven't had very many pumps in my experience, usually morphine PO or SL route works fine, or they will need IV push morphine every few hrs or prn, but every once in a while I come across a pt with such significant pain that they need a pump.

I have a pt now who needs a pump and does not have a port, the dr wants him to get a PICC line in order to get him the morphine pump he very desperately needs. The pt is willing to go through this, and he's going to do it, but my question is.. why can't a drip be given through a peripheral IV? I understand the IV will need to be changed and could infiltrate etc, and were trying to prevent tons of needlesticks for the pt, but I feel terrible to have a hospice pt go through the entire PICC insertion. I feel dumb asking other nurses I work with because I feel like i'm missing something obvious. Has anyone had any experience using a morphine pump/drip with a peripheral IV? why does it HAVE to be through a PICC or port?