Add fields to MEDRUCK_PDF in SFP

I have created a Purchase Order form using Form Builder (SFP).  I would like to add Material Group Description to the form but that field, WGBEZ, is not in the list of fields available in the Context tab.

Right now, I have added an import table parameter in the MEDRUCK_PDF interface that has MATKL and WGBEZ.

I think I need to add code to populate that table somewhere in the Print program, maybe in FM06PE04.

Anyone have any experience with this?  Or am I boldly going where no ABAPer has gone before???  :-)

Thanks,

Chris