AFAIK, there is no 'reverse' replication ...
You may want to define a repliacation subscription with server b as source and server A as the target. Switch this on only when you failover ... When server A comes up, start apply to copy to server A (during which time replication capture from A to B) should be seitched off ..
Once you switch back to server A, ...
I'll stop ;-)
I think, you'll get the point
BTW, I have never tried this ... Just a thought ..
Sathyaram