When making labels for posting letters, I have a data field in my excel table
which has the address data in the following format:

" Mr A B Bloggs, 12 Nowhere Raod, Somewhere, Shireshire, SN12 4UP. "

How can I point word mail merge at this data field and get it to insert a
line break where it sees a comma? so that there format becomes:

Mr A B Bloggs
12 Nowhere Road
Somewhere
Shireshire
SN12 4UP

Any suggestions/solutions greatly appreciated.