I discussed this with some peers, and the consensus is that it won't work with BGP since BGP is not an interface-oriented routing protocol like the IGPs. The IGPs are enabled on an interface so they know which interface has the peer's link-local address. In fact, IGPs they use the link-local address to connect to a peer.
BGP, on the other hand, is not enabled by interface; it is given a neighbor address. BGP cannot tell which interface has the link-local neighbor address since all the IPv6 interfaces have the same link-local subnet (fe80::/10). BGP connects via TCP (Layer-4) so it needs a distinct address with which to peer.
Without trying it, I can't tell, but it may be possible to set a static route to the peer's link-local address, but I seriously doubt an ISP would go to that effort for a non-standard configuration on a POP router that may have multiple WAN terminations from multiple customers.