[Users] Connecting unrelated messages to become a thread ?

[mi]

Hello,

i have to organize some traffic now and there are mails sent by a web mailer which 'belong' to the same person i'm in direkt email exchange. I won't create folders for single persons or addressbook groups because it's all volatile and the whole thing will be over in a few weeks.

-> Is it possible to connect such a webmailer msg with a 'private' one, or more generally, two unrelated messages,  so they appear as a thread (i.e. onbe as reply to the other), maybe by manually hacking the headers ?

Or does anyone know a better method ?

Regards --Micha