using virtual_uid_maps with maildrop transport

[Marvin Renich]

I would like to use something like

virtual_mailbox_domains = domain1.org domain2.org
virtual_uid_maps = hash:/etc/postfix/virtual_uids
virtual_transposrt = maildrop

with

maildrop  unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${user_from_virtual_uid_maps}
  ${user} ${domain} ${extension} ${recipient} ${nexthop}

to have some users of the virtual domain be mapped to regular local
users who may set up their own .mailfilter, but other users will be
mapped to a vmail user whose .mailfilter will sort the mail
appropriately (with an appropriate dovecot configuration to serve the
virtual users).  There may be more than one vmail user (vmail-domain1,
vmail-domain2, etc.), each serving a collection of virtual users.

Can I use the result of the virtual_uid_maps lookup as the -d argument
to maildrop?  Is there a better way to do this?

Thanks...Marvin