Since the inner diameter of both the reedwrangler and a Yamaha Pianica is 1/2″, a short piece of 1/2″ diameter rubber or plastic tubing can make a connection. I just tried it with a piece of rubber tubing. It can be played that way, but the reedwrangler dangles even if the fit is flush, due to the flexibility of the tube, and the connection comes apart too easily. It seems to me the solution described by Joan will have the same issues, and also that its workability will depend on the brand of melodica (the size of the mouthpiece hole). For the Yamaha, relatively hard tubing should work. It’s also important that the mouthpiece with whatever fitting should be easily connectable and disconnectable, unless you don’t plan to be putting the melodica in its case. A firm but detachable connection is necessary.