Some old remote control boats didn't have sail servos, just rudder control. I had one back in my youth. (a very long time ago) The sails just flop around and you do the best you can with the rudder. As a kid, it was great fun, not so much now.
Servo trays can be purchased at hobby shops and bonded to the inside of the hull, but you mentioned you don't see any room in the hull. I suppose you could engineer a deck or simi-deck mounted set up, if the urge to make this boat functional is strong enough, Logic suggestsrelocating the rudder servo aft to makeroom for a sail servo mount. It is pretty much a question of how handy are you? Taking everything out, starting over makes some sense. The old servo may have to be replaced in addition to a new sail servo - once the engineering has been done.
If you are not attached to the boat, you can try to sell it - these forums all have classified sections -
E-bay charges some fees for selling things but can get you some exposure. Food for thought.
Hope you visit the other forum - should help you get some information
Windchaser (here) Boomer there