sendmail masquerade envelope only

Hi all,

I need to know a way with sendmail to masquerade just the envelope (return-path). Our Mailserver validates this adress, but some scripts use the From-Header and need to know the machine where the mail comes from.

Does anyone know how to configure this?
Or ist there at least a possiblity to set a realname in the genericstable?

Thank you for your help