layer 2 question

hi there, i’ve got this escenario:

two RB750G connected in the same broadcast domain by two point-to-point link builded with SXT-G, one link active and the other passive backup, all done with simple RSTP interface priority on the two 750.

Now i want that traffic ONLY for/from and ip, or better a mac-address, is forced to pass always in the backup line, all have to be done at layer-2 level.

It’s obvious that i cannot use RSTP, but how can i do this?

Any suggestions?

ping…pong…ping