what versions of virusscan are you using? If you are using 8.5 and above you can try pointing ePO to V2 dat site which could make the replication size a bit smaller.
How many machines are located at this remote site?
Is it worth having a repository at this site? Can you not just point the machines directory to the ePO server?
Thats what I am doing, its not worth it trying to replicate over 100MB to a site when the machines can just download 100KB over the WAN instead.