I wouldn't. I'm not sure how easy it would be in any event, since server.xml is an XML file digested by Tomcat, not a general-purpose script.
However, if you create a file in the TOMCAT bin directory named "setenv.sh" (Unix/Linux) or "setenv.bat" (Windows), you can assign environment variables in that file and the catalina script will use them.
The file format is the same as any other script file that sets environment variable values.
One of the most odious afflictions that Business has inflicted on the modern English language is "pro-active". Most of the time it's simply redundantly used in place of the simple old word "active". And a good deal of the rest of the time it means "You're not overworked enough yet, so go out and find more!"