How to capture DFF of length 120 character in AR AutoInvoice FBDI for multiple lines?

We have requirement to capture 4 separate DFF of length around 120 character for each line, Line Transactions Flexfield Segments have limitation for 30 characters so not possible in that and tried also Invoice Lines Flexfield Segments but it through error of "Duplicate Invoice Number" becuase of grouping not possible seems.

Anyone came across this situation, knows some solution?

Thanks