Remote server backup

Hi all, we have a following scenario in my company

1. Server A with 2010 R3 installed that backups itself daily on an attached USB drive

2. Server B with 2010 R3 installed that backups itself daily on an attached USB drive

I need to connect another USB drive to the server B and backup bothe servers A+B onto a new USB drive for a remote off-site storage.  

When I try to backup server A from server B I get an error message telling me that the job cannot be completed because the remote computer has already a copy of 2010 R3 installed. 

Are there any workarounds for this?

Thx

p.s. Both servers are Windows 2008 R2