I just found a very smart solution for the T-foil rudders on TheDailySail:

http://www.thedailysail.com/ism/articles...ment&Page=1

As you see the idea is to separate the foil from the rudder blade.
Doing so you can have the advantage of the T-foil without the disadvantages (read drag upwind).
For sure it is appliable (even if not very easily) to beach catamarans.

It was developed by the technicians within Baron Rothschild's Gitana team.
The secret weapon appears to be a T-foil, raisable in a similar way to an outboard bracket. This is mounted on the transom (aft of the rudder) of the starboard hull on the Gitana trimaran.