First off: if they are his aliases and are not necessary for the working of the system as a whole they have no business being there. They should go to his profile, rc-script or whatever he uses to configure his session. I would make that absolutely clear to him in your position.

This is something that always put me off on Linux systems: instead of putting what is absolutely necessary into the systems configuration and letting everybody take it from there Linux distributions have usually some guy force what he thinks is fine onto the whole world.

Using sudo you can find out "where you came from", that is: which user you used to switch into that UID. This way you could set up some mechanism which one (out of several) configurations to apply, as RudiC already hinted at. (Again: only, if his configuration is not mixed up with the systems configuration, so no putting what belongs to /home/<someuser>/.bashrc into /etc/bashrc (or similarily general configuration scripts.)

Second: you can use the "SETENV:" and "NOSETENV:" directives in /etc/sudoers and their respective commandline equivalents ("-E", etc.) for sudo.

I hope this helps.

bakunin