Expressing how soon?

My lil man is a week old, and i seem to have a very good supply going Oh is desperate to feed him been advised not to offer a bottle of ebm for a couple weeks to get bf established - my question is can i express after feeds to start a supply in the fridge, figured its only what lo has left after that feed so wont effect my supply, if anything will it increase it slightly as the breast has been emptied, any help would be much appreciated