Determine if process is running under ExternalTask

System

It seems that when a process running as an ExternalTask calling CLTs needs to redirect STDERR to a file or it is not available - just doing

my ${ouput} = `cmd 2>&1`;

will not trap STDERR (at least under TeamSite 5.5.2 on Windows 2000). I have a module that is intended to wrap all CLT calls and performs this redirection. I don't want to create temp files unless they are really needed - I would prefer to redirect STDERR to memory (such as the line above) and just read that if the module is not being called by an externaltask. Is there any way for this subroutine to determine if it's being invoked from an ExternalTask script or from some other process like a CMI or scheduled task? I mean some environmet variable or other method? RIght now I'm setting my own environment variable at the beginning of the ExternalTask scripts and the module checks that, but I'm wondering if there's a better way.