Snake some safety wire through the stick, attach end of safety wire to end of PTT wire, and pull safety wire back out. OR Tie some monofilament fishing line to a small cotton ball and vacuum or pressure blow it through the stick.
Using a vacuum to suck the pull string from the top down works great. I would suggest using a more durable pull string .... I used a waxed cord that is commonly used for making jewelry, very tough stuff.
In my case, I installed Tosten CS-8 grips and pulled additional wires for all the switches ... quite a tight fit around the 90° bend inside the RV-12's control stick. If pulling additional wires, I wholeheartedly suggest placing the wires in expandable wire sleeving ... when pulled, it acts like a "Chinese finger" and grips the wire bundle tightly. Pull firmly on the pull string while assisting the feeding of the wire bundle from the bottom of the control stick.
Thanks everyone. I uses a vacuum to suck a thread through and used that to pull a string. However I found using any knot and it would get hung up. I went to the universal backup, duct tape. But the duct tape was too stiff to get around the corner. Brilliant wife came up with the idea to use sever small widths to tape with spacing between so if would be more flexible. Success!!! Appreciate your spouses.