OK so here we go, you guys are sisters so I'm assuming you've had fierce battles about bathroom time for your whole lives. Get this santa toilet cover and keep it hidden in your bathroom. Wait around and kinda watch and when she goes to the bathroom slip in front of her. This will get her angry and she will think you're just being the annoying sister like when you were kids. Now put the cover on the toilet, and put the tickets in his mouth. Turn the lights out in the bathroom when you leave and she will prolly scoff at you or something, then wait outside for her to close the door and turn the lights on, find the tickets, hugs kisses, etc.....?
Idk I'm a guy so maybe my idea of a fun gift giving thingy is all wrong or cheesy, but its all I could think of on short notice.