Wouter,

If you want a spinaker halyard and two trapeze lines to work with a sleeved main, it will be necessary to attach the three of them to the mast after it is already inside the mainsail sleeve. It can be done if the main is like the Laser, without halyard.

In this case one alternative would be a furled spi or screacher without halyard, with its top swivel attached directly to the mast. The spi/screacher would be furled for upwind sailing. Maybe its foot could be attached to a forward bridle instead of more complex pole?