dovecot - Aug 2015 - Dovecot proxy and password scheme updating

Hello,

I run a dovecot proxy (which is doing authentification itself) and a
dovecot backend on separate boxes.
I want to change the actual password scheme.

Since postlogin scripting is not supported by proxies and %w variable is
not forwaded to dovecot backend is there any way that I can update the
password scheme with my current setup ?

Thanks in advance.