Just an idea: why not using the fastest link (10G) between your two sites as the main active link and leave the slowest one (1G) as the backup link?
I think with STP priority you can manage that...or try to see if (old) HP Smart Link approach (Master/Slave ports) could be adapted to your scenario.
I recall I've discussed (theoretically only) a HP Smart Link case here three years ago but I had no evidence it ever worked...still I'm not totally sure it can be applied on a scenario where there are just two switches involved (1:1) among which one want an active and a backup link for a group of VLANs.
Probably the STP approach is still be the best one IMHO...one link up the other blocked (no bandwidth aggregation but a minimum of resiliency in case the forwarding link will go down).