Theres a couple of ways I would try it. The first would be to use multiple XRecords with keys of "Doc1", "Doc2", through "Doc(n)" to allow later iteration, each with a single ( 3 . "DocPathHere") element. The other would be to have a single "MyLinkedDocs" XRecord with multiple ( 3 . "DocPathHere1" ) ( 3 . "DocPathHere2" ) ( 3 . "DocPathHereN" ) elements, each pointing to a single file. You could then pull all "3" prefixed items from the assoc list for later processing. If needed they could be surrounded by a DXF 102 group to localize them.
The choice of DXF code depends on whats being stored; 3 is good for a path name, but if multiple text items were being stored I would consider using unique codes from the 300-309 sequence.