I don't think combining both fields into another field and set it up as Primary Key is a good idea, because in a real world, there are many tables that have multiple fields as Primary Key, not only two fields, sometimes the tables have three, four, or five fields as Primary Keys. Combining all those fields into one field is neither impractical nor effective.
Do you have a plan to support multiple fields for the Primary Key? Because PHPMaker can do this nicely. PHPRad should support this feature, too.