This repair shouldn't take longer than 15 minutes. (That is if you allready have the parts)
Step 1: The parts
2 Meccano Bolts
2 Meccano Nuts
The tools I used were the standard Meccano screwdriver and wrench, a knive, a screwdriver and a drill.
Step 2: Take the headphones apart
Remove the cussion in the center. With this Sennheiser model, the cussion is glued to the headphones. Pry it off carefully.
Note: Be careful not to lose the tiny screws!
Step 3: Start repairing
Once you think you've got the right shape, measure where you will need to drill the holes in the headband.
Once the holes are drilled, insert the bolts through the headband and Meccano strip. I preffered the nuts on the inside.
Step 4: Reassemble
Important: Make sure the wires aren't twisted when you put it all back toghether.