Trouble with multithreaded sequence diagram

[mgaulin]

I'm having a heck of a time keeping the activation rectangle on a lifeline connected between two messages that I want to be part of the same activation. One message is a call, and the other is a return. If any other messages are on the diagram between the call and the return then the existing activation rectangle is split into two.  I know about "extend source" and "end target", but they do not do what I want; I sort of want "extend target" (to keep the activation rectangle in place down to the next message). This is a multi-threaded situation, so things are not strictly in sequence, and any interleaving messages appear to break the activation rectangle.

The other UML tool I use has explicit control over the activation rectangle that I think AE doesn't have that; it appears that AE wants to control the rectangle via logic and I don't know how to make multi-threaded stuff fit.  

So, is there any way around this?

[TrtnJohn]

There is no message between objects for a return.  Instead, the activation bar on the lifeline of the message indicates when it will return.