I have just posted an alternative method that does not break the template concept of avoiding mixing PHP into your HTML.
Edit the "public function tpl_defaults()"
add this to the bottom of the function:
Then in your templates you can use
<tmpl_var format="strtoupper" name="cpuser">
for example alongside the word LOGOUT in main.tpl.htm
Hopefully the 'bosses' will include my suggested change to app.inc.php in future versions!