Migrate SQL Server database to multiple files (shrinkfile emptyfile vs log shipping)
In a word, no.  You have to do it live.

What you'll want to do it add 3 new files.  Then simply start doing index rebuild operations.  As long as you are doing rebuilds not defrags SQL will start spreading the data across all the data files.

I'm assuming that you are running on SQL Enterprise Edition and can do online index rebuilds.