Actually you do know such an enduser: me. I have two lines coming into my home and I run IPv6 over both of them. In fact the server that is colocated with one ISP is reachable (over IPv6) through the other ISP, my home network and the link to the colo ISP. (Do some traces for www.bgpexpert.com.)
Then....What's the matter ? I didn't quite catch what you need. to set up this topology. Do you need a higher block of IPv6 addresses ? or it's that you need to manage your own routing ?