IRULE: TCL Error when trying to invoke STREAM expression.

That SOL made me chuckle a little. It hadn't occurred to me to use a layered VIP to fix this, and I'm not 100% convinced that it couldn't be solved without it. I do know that the problem indicated in the SOL is still there in 11.5 and that it only manifests (oddly) under certain visual policy configurations. So in any case, a layered VIP should indeed solve the issue. Put an LTM VIP on the outside, with your STREAM processing iRule, and send the traffic to an internal APM VIP. You could alternately put the APM VIP on the outside and the LTM VIP with STREAM iRule on the inside.