[exim] OT - setting vacations

This is a bit off-topic so apologies in advance.

exim 4.43 on slackware 9.1, Qpopper version 4.0.5, MMDF mailboxes, 50
users.

All the users run a version of MSWin on their desktop. Not one-man-
jack has a shell account but they want to be able to turn on their
own vacation messages (can't be a bad idea).

The way I do this at present (on a v3x system) is to have a system
filter in the directors section of the config that resolves the alias
and then looks for a filter file with that name in a specific
directoy. Ala:
central_filter:
driver = forwardfile
file = /usr/var/adm/exim/filters/${local_part}
no_check_local_user
no_verify
filter
allow_system_actions
user = mail
reply_transport = address_reply

And I have to create the files for the user.

Does anyone have any suggested ways to allow users to turn-on
vacations from a windows desktop?
Thanx.
Dp.