Hi,
You can configure Static Policy NAT on your site and the remote Site B has to configure NAT also
Your sites configuration could be
access-list SITEB-POLICYNAT permit ip 10.1.1.0 255.255.255.0
static (inside,outside) 20.1.1.0 access-list SITEB-POLICYNAT
If some hosts have Static NAT configured on the network 10.1.1.0/24 you might have to remove the Static NAT and enter it again right after that. This is because without it the Static Policy NAT might not take effect.
- Jouni