Call a function module from within a sapscript form

not being an ABAPer i have the task of changing the Invoice SAPScript form.

i have made the necessary changes - just about... but they have asked that i include the VAT Number on the Invoice....

not too bad apart from different company codes have different vat numbers...

not knowing a better way to retrieve data from table V_001_B - i am using the print program -RFKORD50, is there a better way of getting the VAT Number by company code? I figured if i could call the FM to return the value, all well and good.., they do not want the print program changed if possible so was looking at alternate methods....

or am i trying to reinvent the wheel here?