Splitting files in Mercurial and retaining history on both sides

I need to split a number of files and I'm looking for options to retain the full file history in the split-off files.

Background...

I've inherited a project containing lots of Oracle PL/SQL packages with the package spec and the package body all stored in a single ".sql" file. I'd prefer to have the package specification and package body in separate files.

i.e.

Starting with: myfile.sql

I'd like to split this file so that the first bit (package specification) goes in:

myfile.pks

and the last bit (package body) goes in:

myfile.pkb

I've no issues doing the separation itself, but I was wondering if anyone had any ideas how I could retain show the file history of myfile.sql both in myfile.pks and myfile.pkb.