This came up in another thread and I figured out a solution with the command-line:
tasklist /v /fi "imagename eq outlook.exe" /fi "memusage gt 524288" /fo "list" | find "User Name:" > temp.txt & for /f "tokens=1,2,3" %a IN (temp.txt) DO ECHO %c
That will return a username if an instance of OUTLOOK.EXE is using greater than 512MB of RAM. Otherwise, it will return "INFO: No tasks running with the specified criteria."