I've got the same, several emails that are only forwarders onto others.
In the mail clients I set up several different email accounts, one for each of those addresses; however the "forwarder" accounts are not set to send/receive.
When I want to send a mail from a different mail address I can just change the sender in a drop down box. I use outlook/outlook express/evolution on the various computers and it's the same in all of those.