showing an recipient that doesn't receive the mail

[Nils]

Hi,

    when composing an email, can I assign the header value "To" in a 
way that it is shown by the email client but ignored by postfix?

    I've created a php-cronjob for a customer, that fetches mails from 
an imap box (mta is postfix), recomposes them and forwards them to a 
list of recipients. Mostly like a mailing list would do. Now the 
customer doesn't want the final recipients to see their own addresses in 
the to-field. Instead he wants the from- and the to-field of the mail to 
seem unchanged. How can I do that without looping?

Is this even possible without touching the postfix configuration? If 
not, how would I configure postfix to make this possible?

Kind regards, Nils