I've ditched the gate idea, too hard to make it work with an internal track.
We got inspiration from Nigel and Cory on Katana ( Sunfast 3600).
We're putting an eye bolt at the second spreader and rigging an prestretched 8mm dynex strop with a rigging screw at the base of the mast.
It will work the same way as a separate trysail track, we can hoist the trysail on the topping lift or the main halyard. in addition its removeable, light and easy to rig. The Trysail will be rigged with soft hanks.
I reckon its a good option.