Escape comma in the LDAP passdb subquery configuration

Hi I have to configure the LDAP passdb to execute a subquery defining dinamically the new DN to use.

For example: pass_attrs = @mail=mail=%{login_user},dc=%{login_domain},dc=example,dc=com,
=proxy=y,
=host=%{ldap:mailHost@mail}

In the previous example, the problem is the use of "," for DN representation, which is also the separator for the attribute template in the pass_attr parameter value. I tried to escape it with '\' or '%' but it doesn't work. Dovecot version is 2.2.13. How can I resolve this issue?

Thanks in advance