Having thought a little more about this (and pondering the other replies)... how about this (untested):

• have .profile execute a perl script of your own design
• the perl script presents choices, requests a response, checks that the response is valid
• based on the response, create a copy of (or symlink to) the selected setup_env file in the user's home directory , e.g. as $HOME/.chosen_setup_env
• after the perl program exits, .profile goes on to source $HOME/.chosen_setup_env

The point is that, as far as .profile is concerned, the environment settings are always provided by the same file that it finds in each person's $HOME; you just need the perl script to allow people to control what that file contains (or what it points to) at login time.

This might have a nice side effect: folks who want to use the same environment file as last time could just reply to the perl script with an empty line (just hit <return>). The perl script only needs to create a new one when the user specifies a particular choice (or when the user doesn't have a .chosen_env yet).