Adding Columns to System Form Matrix Possible?

Hi,

I have a situation where I need to add custom fields to extend the functionality of the Freight Setup (OEXD) SAP doesn't allow me to add UDFs to this table so I've created a UDT which will contain a UDF to link to the Expense Code in OEXD and then the other custom fields I need. Is there anyway I can add these columns to the Freight Setup form's matrix so it's there for users to enter and then I can capture the form data events in order to save my custom fields at the same time as the form saves?

I've already tried to add columns on Form Load but it complains I can't add columns when there is already data in the matrix.

Any thoughts?

Thanks,

David