[Koha] Split Call Numbers--Variation

[Anne (library) Warrington]

Since splitting call numbers has come up, can anyone tell me what to do 
with a non-classification number call number? My Library of Congress 
numbers split mostly OK but my fiction just uses three letters of the 
author's surname, i.e. FIC SMI for "Fiction Collection" author "Smith." 
No matter what I do I can't get the spine labels to print as follows:

FIC
SMI

Any suggestions?
Anne Warrington