If you add a target to a targetlist after the beginning of a campaign, and the initial sending of an email marketing, how can you send this target the email marketing, without resending everyone the email again?

sample: you have a discount untill the end of april 2007, and everybody that you add to your targetlist for this discount campaign, untill the third week of april, should get the mailing about your discount.

I am on 4.5.0h