You are not restricted to the four variables in the Personal tab in User Preferences when it comes to User Variables.
Create extra variables by amending the username.ini file. (Bob.ini, John.ini, etc.), which can be found in your GoldMine root directory: C:/Program Files/GoldMine or G:/GoldMine, etc.

Create your own custom user variables under the [user_var] section

e.g.
[user_var]
Birthday=8/13/1978
DateEmployed=1/1/2001
Title=Sales Manager
Name=John Doe
Fax=(888) 232-3433

These can then be referenced in email templates and mail merge forms by using the following coding format:

<<&User_Var.DateEmployed>>
<<&User_Var.Title>>
<<&User_Var.Fax>>