Some sellers are offering some credit at closing. With disclosure upfront about being in the WPCA area (which is always done) they let the buyer take on the responsibility. I'm not sure if the cost can be rolled into the purchase financing package though.
Check out this link for some explanation on funding the work which is spread out over several years http://www.oswpca.org/PrinterfriendlyFAQs.htm
Hope it is helpful but contact me at firstname.lastname@example.org if I can be of further assistance.