Synchronizing 2 Usrp2's via MIMO cable?

We need to synch up multiple U2’s.

I’ve seen reference to using the MIMO cable to sync 2 U2s.

Is this currently supported by the existing software?

If so, what do I need to do in my own code in order to affect a sync?
Would the same code work with a GPSDO (e.g., Jackson Labs FireFly (which
I’ve also seen referenced here by Matt & others))?