Assign leads based on zip code range

Hello,

My client is currently running SugarCRM Professional 6.5.12. They want to associate their US sales reps with territories, and those territories are defined by zip code ranges.

For example, you might have a rep who handles all of northern California (9320---93601, 93399---96699), northern Nevada (89301---89999), and New Mexico (87001---88441).

I created a new workflow definition for this, and created a condition where Primary Address Postalcode Equals 00000. I then created an action where the lead is then assigned to 'Administrator'. This workflow works properly, and if reps were simply assigned by state, I could enter 50 static conditions and 50 static actions this way.

Since the workflow condition only accepts 'equals' or 'does not equal' as operators, I can't use this to define zip code ranges. Is there another way I can accomplish this goal? Would it require upgrading?