TC detect a new changelist outside P4 workspace mapping

Hi,
I have a specific problem with Team City and Perforce;

Our builds in TC are using Perforce as VCS root.
The mapping of the workspace (Client mapping) is as following:

//depot/PR_main.br/... //team-city-agent/...
-//depot/PR_main.br/Testing/... //team-city-agent/Testing/...

Team City detects change in the VCS only when there is a change in PR_main.br,
but does not detect a change in PR_main.br/Testing.

Unfortunately we need somehow make TC to detect that there was a change also in the PR_main.br/Testing,
since TC triggers (after a build which does not require the Testing) another action outside the TC.

The PR_main.br/Testing directory is about 30GB large, so including it into workspace is not acceptable solution.

Have you any ideas how make TC detect a changelist that happens in the PR_main.br/Testing?

thank you,
--Pavel.