InfoPath Dev

I am building an InfoPath 2007 form template for a purchase requisition form that will be filled out using the InfoPath client (not web-based).

I have an "Account Number" drop-down list in which I have created an external lookup to a SharePoint 2007 list.  Here's my dilemma:

The drop-down list is a list of account numbers, but I want to filter the displayed choices based on information from both A) the SharePoint list and from B) another drop-down field on the same form. 

A)  The SharePoint list is a list of the account numbers and several Yes/No (check box) columns named for departments.  In this list, the check boxes are marked for each Department that is allowed to charge to the correlating account number.

B)  The other drop-down field on the form is to select a Department.  These Departments are named exactly the same as the Yes/No columns in the SharePoint list.

My question - is there a codeless way to filter the lookup values on the "Account Number" drop-down by matching the selected department (from the Department filed) with those Departments on the SharePoint list with the check box selected for the corresponding account number?

Well, I did come up with a workaround.  I just made 10 copies of my Account Number drop-down (for 10 Departments), and ran each through the SP list for its respective Department.  I hid all copies except for the one for the selected Department.  Was there a better way to do this?