Timbo is on the right track here

Hinge it off the mainbeam with a retainer line of the spi pole. This line will allow the AoA to be set. Place the foil at the tip of a round alu tube and make a loose sitting fairing from foam that youbslide ove the tube. This fairing will weathervane around the tube and thus not act as a daggerboard. As a result this appendage will not be loaded up much in the sideways direction. Two dyneema line may be run from the mainbeam just inside the hulls to the tube just above the waterlevel and thus make for a low cost hinge mechanism and sideways support.

When traversing the surf and landing just pull the foil horinzontal towards the spi pole and clear of the water.

The T- foil may be made of a single 300 by 100 mm piece of multiplex shaped by hand and glassed over. Fit it to the end of the support tube in such a way that it can rotate freely downwards with its trailing edge but never upward past the horizontal. That way the foil can never pull you down. The hinge needs to relatively closevto the leading egde for this. About 25% - 30% down the foil.

A simple rubber end stop will suffice to prevent rotation upward.

At relatively slow speed you pull the assembly a little forward thus maximizing AoA, with increasing speed you relax the line progressively thus reducing AoA and preventing excessive drag and pranching. Fiddle about with a bungee in parallel with the retaining line and get an automated AoA sytem, one that also recognizes pranching by the excessive drag that is associated with it and adjusts the AoA accordingly.

Hell, this may actually work !

Note how even a small diameter tube will be able to withstand the 30-60 kg buckling load. And how a single foil in the middle off the boat with twice the area will have exactly the same overall behaviour with respecttomrighting moments etc as two foils half the size at the tips of the daggerboards.