Then it looks like you are not going to be able to influence the SAL in this regard. There are kernel functions behind the collection and you will not be able to enhance them.
RAL docs there are a few of them here on SCN. It was a customer development originally as far as I know, but then SAP decided to make a product out of it (so it has a price tag on it).
Personally I would recommend that you open an OSS message with SAP and request that the field type be changed to a longer one and that SAL also sends a longer path. 255 is the normal length for type FILE so they should have taken that in the first place.
Little tip: it being a Friday afternoon, use priority LOW. Those are like little snacks before going into the weekend. Other priorities will be dealt with next week... :-)
Cheers,
Julius