How to split a patch

Hi all,
I have a big patch that affects a single file that needs to be split in
a few logical patches.

I know ho to do the opposite process, rebase -i and squash is something
I'm really used to do but this time that trick is not going to help me.

What is the preferred way to split a big patch in a series of smaller patches?

Thanks.

Ciao,
-- 
Paolo
http://paolo.ciarrocchi.googlepages.com/