Use of constraints in SAG

Hello.

Has anybody seen such trunk configuration: a customer uses 3 IP addresses on its side, thus on SBC we have 3 session-agents combined into SAG "customer". SBC provides surrogate registration for the Customer. Number of active sessions must be limited to 30 for the Customer and we set the constraints "max-sessions=30" on each of three session-agents. As we can see, in normal case, when state of session-agent SA1 becomes "constraints exceeded", SBC automatically sends next call to SA2. Theoretically when Customer gets 503 to its INVITE on its first IP, it automatically re-routes the call from the second IP and SBC accepts it, because SA2 from SBC's point of view is still in-service. Our purpose is to force SBC to stop recursion from SA1 to SA2 when SA1 becomes "constraints exceeded" AND to reject the incoming INVITEs from all three Customer's SAs.