share Themes / plugins files for several install

Hi all !

Well, here the point.

We are setting up now 5 WPMU sites. All with the same theme library. (some wont be activated since the farms are thematic)

Is there any way to have all of theme in one unique folder in order to share it and not have 5 copies on the same server or would it be to complicated to recode the theme path ?

I found that but not updated

Sincerly it would be just... great to share one only folder
One single update for all farms...

I dream a lot in those time isn't it ? Just a little plugin ? hum ? Theme path must be defined somewhere once nope ? so any install could share the same directory....