Changing IP using "NeighborNet"

[hangten]

Ok so I have a question with changing an IP. Heres the lowdown, My neighbor and I have a great friendship, he lives out of town and his house next to me is a summer house (he only comes in the summer) and once a month in the winter, other then that ill watch for intruders etc. He has a wireless router which enables me to use his internet. Well needless to say while using his IP I have gotten suspended from ebay.

My question is how can I get a different Ip address while still using his router and without him knowing?
I understand that the ip address is from the router alone, but is there any program that i could use to change it?

How about VPN? Do I have to have access to his router in order to use it?

Thanks doods!