[Zope] How to include packages in INSTANCE_HOME

Trying to set up my sites to run as "INSTANCE_HOME" I have a few packages that is defined outside the Products directory, like: "<ZOPE>/lib/python/mypackage" I have tried putting these in my INSTANCE_HOME directory, but my products cannot find them. Isn't it possible to do it like that? Do I really need to install those packages under my Zope install, or should I just put them in a special directory? or? regards Max M