Possible? Sure. Good idea? No...
Gasses flow similarly to water and 90 degree bends will ruin your airflow.
Having never messed with a 126 I'm a little out of my element but as nobody has yet replied...
On a 123 the "center" muffler actually lives way up front, pretty much under the passenger seat. The exhaust then goes across the car to the rear muffler which is on the other (driver) side of the car.
So rather than crazy 90 degree bends just get a muffler, cut a muffler size hole in the pipe you've already got and insert said muffler inline.
Unless the car is real loud I probably wouldn't worry about it. I *think* you've got a 617 engine and in my experience the engine part of the car is louder than the exhaust part of the car anyway. My wagon lost its rear muffler once and we drove it for several months with just the center muffler, it was a little louder but not bad...
My 240D has a leak where the manifold meets the exhaust, I presume theres a gasket that goes there (haven't spent any time on it yet) but when the engine isn't totally warmed up it makes noise when I'm on the throttle (most of the time in a 240D
) maybe you've got a similar issue?
HTH!