I have done two things depending on what the client prefers. I *think* I've done this for PR. I know I've done it for new framework modules.
1. Create a new field for full last name. Fill out BOTH original and new field. If there is something in new field, that is the one that gets printed on check. Otherwise , original field. Or
2. Create a new field that is the part of the name that cannot fit. In this case , concatenate the two fields in printing.