[Dovecot] dsync conversion and ldap attributes

I have:

mail_home = /srv/mailstore/%256RHu/%d/%n
mail_location = maildir:~/:INDEX=/indexes/%1u/%1.1u/%u

userdb {
	args = /etc/dovecot/dovecot-ldap.conf.ext
	driver = ldap
}

and the dovecot-ldap.conf.ext specifies:

user_attrs = mailMessageStore=home, mailLocation=mail, mailQuota=quota_rule=*:storage=%$

Now I want to convert individual users to mdbox using dsync, but how to I tell location2 to not fetch "home" and "mail" from ldap and use different mail_location (mdbox:~/mdbox) ? I.e. I want converted accounts stored in mail_location mdbox:/srv/mailstore/%256RHu/%d/%n/mdbox.

-jf