I am more familiar with solaris but I will give AIX a shot:
The following is based on AIX 5.1.0:
You can try the global environment files:
/etc/profile and /etc/environment - just modify the script to check for the user(s) you want to include in this group. Also, there is a skeleton script file created under /etc/security/.profile. A configuration for security exists for users under /etc/security/user.
Well, I hope this helps. I have used the /etc/profile script to add additional functionality to help me with specific users.
Good luck.