There seems to be an easier way of doing this:
In the manual User_Management_v10.5.mnl.pdf you can find a section 'Using the Preference Editor to Manage Core Services' on page 236.
Using this information it is quite easy to assign preferences in the workgroup manager.
The cool thing about this is that you may use '%@' as a variable for the login name.
This way options such as the account name for login into the mail server may be used.
If I were given the option to post a few picture I could illustrate this.
Feel free to contact me for more information...