Parhaps a late response.
Have you tried filtering the GLBP traffic between the two DC's so that the GLBP negotiation remain local within a site and each site elect a local primary.
Config similar to the following might work. But I have not tried it...
mac access-list GLBP-MAC
1 deny any 0007.b400.0000 ffff.ffff.0000
2 permit any any
interface e2/1
mac port access-group GLBP-MAC