Hi rubantin, i am sorry to read of your loss and i admire the support you are given your dad, even though you live in different states just think that really your only as far as the phone is away from each other.
The only thing that comes to mind that might help his pain is a T.E.N.S machine
http://www.mydr.com.au/default.asp?article=4198
I also agree with Aussie, that a pain doctor might be able to help him more so than General Practitioners can.
good luck, i hope is able to get some relief soon.

Brian