Several options to 'workaround' this:
a: Present Outlook as a published application (or part of published desktop) under citrix or comparable serverbased-environment and store the cached files centrally.
b: If using Windows: create roaming profiles for your users that point to a centralized location for their outlookfiles.
Don't know how to work with something like roaming profiles under linux but expect it must be possible..
option a maybe not applicable but option b should be..
Hope this helps.
Using ZCS Network-edition 5.0.16 on Ubuntu 6.06.2 LTS and 8.04 LTS