[Dovecot] variable expansion in dovecot.conf?

hi all,

does dovecot.conf support the definition/use of user variables?

e.g., in principle,

my_DIR = /path/to/something/

then,

default_mail_env = maildir:${my_DIR}/%d/Accounts/%1u/%u/Maildir

or, for that matter,

    default_mail_env = blahblah

then,

namespace private {
    ...
    location                 = $default_mail_env
    ...

i finallly figured out -- through randon thrashing -- that the simple "$" format has been causing me grief ...

and, cursory searching has not dug up anything (yet) in the man/wiki/etc.

possible? reference docs for it?

thx!

(ack to my margarita for now ...)

richard