How to automatically sort an enumeration?

I have a work item attribute type enumeration in my RTC (3.0.1) called customer, which contains around one hundred entries to start with. This enumeration is a drop-down field when creating a new work item, so an end user selects a customer from this dropdown list.
A requirement is that, when adding new values to that enumeration, the customer list is automatically sorted when a new work item is made, even when the values are not sorted in the process configuration.
The way I do it now, is when adding new values, I do this directly in the process configuration xml file directly, taking out the old values first, copy them to excel, add the new values in excell, sort them and put them back in the process configuration file. 
I'm searching for a smarter way of doing this now.
Any ideas on how this could be done? Value set providers? Writing an extension?
Is there a way to programmatically connect to the process configuration file, parse from there the customer values, sort them and diplay them in the workitem dropdown list?
Would like to know in what direction to go when implementing this.
Any ideas? Your thoughts are very much appreciated.
Regards, Luc