Escape comma in the LDAP passdb subquery configuration

[Francesco Fiore]

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