formatting an auto-populating street address in fillable form

I have a form where the addresses auto-populate as a single line like:

1234 Main St., City, ST 123456789

and I want it to show up like

1234 Main St.
City, ST 12345-6789

If I cant break the line between street and city, is it possible to at least add a - in the zip?  Any help with the custom formatting javascript would be greatly appreciated.