[Dovecot] move mail from server with v1.0 to server w. v2.1?

[Frank Lienhard]

I'm about to replace my old server. Both servers are on my internal network.
The old one ist running debian lenny(32bit) with dovecot 1.0.15 and the 
new one debian Wheezy with dovecot 2.1.7.
I set up the users on both systems identically (same gid uid).
My first attempt was tho simply rsync the Maildirs along with the homes. 
Both deovecot versions are set up with the maildir format, but this 
results in ~30% doublicated mails on the new server.
I then learned about doveadm/dsync, only to figure out that this isn't 
available in v 1.0.15 and therefor won't work.
So which could be the most painless way to solve that?