How about let routers accumulate (with XOR or something like that) link CRC (or some psuedo random number involving link specific numbers such as MAC addresses of a hop) into (so far useless) flow label field to let upper layers notice the path change to trigger the transport layer?
I myself am afraid that it is too late to change IPv6 router behaviour. So, I never proposed any multihoming solution involving router changes.
However, I know transport people are actively proposing to change router behaviour to help TCP and they have better chance with IPv6. :-)