Attempting to do what you want, by using tubing to re-rout the exhaust is fraught with danger. The dimensions of the exhaust system in 2 stroke engines and how an engine runs and performs are invariably linked.

Change the dimensions of an expansion chamber by a millimeter or 2 and the entire dynamic of the engine will change, the same goes for the length of the stinger or even the amount or type of packing that is used around it.

Now, currently i am talking mostly from my experience with 2stroke race bike and the amount of effort we put into building one off pipes to give us a competitive advantage, as well as the 1000's of dollars spend on software that would aid us in determining the outcome of various chamber modifications.

2stroke gas engines are much less forgiving IMO, to changes outside the norm. So the only real options you have, are to get a pipe that is designed to give you rear exhaust, or to take to your current one with saw and tig welder to turn it around and make it face backwards.

Anything other than this, and you will find the performance of the car to be totally crap, if it runs well at all.

EDIT: Oh and you would also need to consider the fuel pressure pipe, changing the flow dynamics of the exhaust will also change the amount of pressure supplied to the fuel tank, it does not take much change here to totally wreck the tune of a car.