The lever is a stamped piece, riveted on to a larger assembly. I think you could try a couple of methods to fix it. If you take off the lens mount (5 screws) the lens probably looks like the lens on the left.
The easier fix is to try to glue a lever on to the stub. The replacement lever needs to engage the camera's aperture arm in the same place, so you may have to bend either the old lever or new extension or both to get that location correct. The lever doesn't take that much force to move so it doesn't need a super strong repair, like riveting or welding.
A second option is to remove the stub and put on a whole new lever, maybe with rivets or small screws. In that case you need to slide the aperture ring off, being careful because there is a spring-loaded bearing trapped between ring and lens body right where the orange diamond is on the distance scale. The bearing is in this photo on the lower left.
Then you can remove the screws hidden under the aperture ring, to slide off the rear of the lens body. You're removing the part with the distance scale and white button. It looks like this:
You can see the other side of the rivets holding the lever on. You need that forked piece also. Probably there is room for some small screws to replace the rivets.
The cheap M50/2 lenses use a different construction unless they are really early Made in Japan models. You may not be able to use any parts from the later version except the aperture lever, redrilling some holes. A later M50/2 looks like the lens on the left here, with the aperture mechanism in the center. There is no fork.