Session lifetime issue (post on behalf of)

I'm trying to solve a common problem which occurs when I'm using PoCos.
The crux of the issue is that a session doing a post to a PoCo, needs to
stay alive for work done by a secondary post by that PoCo.

Consider:
    1. Session A posts to Session B
    2. In Session B event handler, it posts to Session C "on behalf of
Session A".
    3. Session B exits event handler.
    4. Session A dies, because it's event was handled by B, but it has no
way of knowing Session C is doing something for it.

Since Session B typically belongs to the "other persons PoCo" (OPPC), I
can't really get inside of
it and change it.  So the solution to this problem must not alter the code
for the OPPC.

This seems to be a very common second order problem.

Is there some standard technique for solving this?  I've looked at few
PoCos for solutions, and
searched for "continuation" like things (e.g. POE::Session::Yield::CC), but
these don't seem to
solve the problem.

Thanks,

Zerohero