Default Signatures for all clients

hi,

we are using outlook 2007 (on vista clients) and exchange 2003. I have to
provide a signature which is equal (exept phone extention an mail address)
for all clients.

but my users always change their signatures, so i have a lot of different
versions. with a outlook 2007 admx setting i disabled the "signatures" -
button in the option menu.

my problem is now, how can i set the default signature without using the
standard outlook gui (option menu - signatures-button)?