How about a telescoping tongue? One made with 2" outside square tubing (receiver tubing) that slides through a larger outside "diameter" tube that forms the backbone of your trailer? You could set it up so you could adjust the length from all the way flush with the tray on the front of your trailer (for storage mode) to about three feet or so out. You could drill the 2" receiver tubing so that you could adjust the length by "X" amount of inches out (say 18", 24", 30", 36") using a 54" piece of 2" receiver tubing (so even at 36" out you'd still have 18" of receiver tubing inside the larger tubing). You would want the larger tubing drilled so there were always two hitch pins securing the receiver tubing in the larger tubing (at least for towing purposes).
And of course with the tongue being a long piece of 2" receiver tubing, you would have your choice of couplers: ball mount, lunette ring, or some sort of multi-axis hitch.