Cisco VPN :: 7301 - Multiple L2L IPSec Sources On One Router

I'm trying to make a redundantish office/datacentre connection on the cheap. At the datacentre, we've got a 7301 (12.2(24)T5) and at the office we've got a Mikrotik RB1200 (5.12).The office router has two ADSL connections to two different ISPs, the datacentre router a single GigE to a colo provider. I'm trying to build an IPSec encrypted IPIP tunnel over each ADSL service to a separate loopback interface on the datacentre router, so I can run OSPF over the top for route exchange. I need to use two different loopbacks on the datacentre router so the office router can have a static route for each out each ISP ADSL. But I'm running into issues making encryption work on two different source addresses.Using the 'crypto map xxx local-address Loopback12' command, I can specify the outbound interface for one of the tunnels just fine, traffic moves as expected - while the other tunnel fails to encrypt. But is there a way of having two peers use two different local addresses, or applying two crypto maps to a single physical interface?