If you have the skills and are creative, you can make one.
To do it properly, you will need the appropriate tap to make a thread for the bolt.
Alternatively, you could use a bolt and nut. You need to ensure it does not interfere with anything.
Understand, the bit that hangs down at the very bottom, is there to prevent the derailleur from rotating forward. You need to include that, or have another method to prevent the derailleur from rotating forward.
If it was me, I would use a larger piece of steel, so you have something to hold on to, or grip in a vice, and cut it off at the end.