depending on how complex of a setup you are willing to deal with, one option would be to startup procomm with a windows batch file initially, the batch file will not execute the next command in it's file until the procomm windows totally exits itself. It takes about 4 seconds for me on a windows 2000 Pro machine for this to happen.
If your logout procedure is adaptable, then have the next line of your batch file specify the path to your procomm executable, so something like "%PROGRAMFILES%\Symantec\Procomm Plus\PROGRAMS\pw5.exe" (include the quotes) followed by the path and name to your .wax file
So taking into consideration if the user had logged out of the system, then closed it, I'd think your system could take the garbage characters that the logout procedure would throw at it.
I use wyse 50 emulation on a Hollander yard management system (ancient stuff), so for me I can close procomm and open it back up and start typing as if nothing had happened (however a screen refresh would be nice).
hope it helps,
dan