You can slightly grind down the diameter of the end of the 1/8" rod, and put a 4/40 thread on with a 4/40 die. Then you can attach the 4/40 clevis of your choice.
Alternatively, you could attach 4/40 threaded rod to the end of your 1/8" smooth rod by soldering brass tubing over the smooth rod end, and inserting and soldering the threaded rod into the tube end. Hope this helps.
RCABS- It's easy to control your own bladder!