I found it fun to go to the bicycle store to buy handle bar grips for the control sticks. I even took one of the control sticks with me and the guy at the shop was intrigued as he had never seen such handlebar.
The fun stopped with step 3 which requires to route the wires inside the stick as there is an obstruction at the bottom very visible on figure 2: the sleeve that gets the bushing does not leave a lot of room to guide the wires. The solution: use a fishing line with a sinker (all out of my fishing box!) and use gravity to route the wire from bottom to top. I found this idea on the VAF forum, my usual source of inspiration.
The next challenge was the installation of the control sticks which requires to drill the bushings at 1/4". My drill got stuck several times as it is difficult to secure the bushing tightly without risking to crush it in the vise. I finally got the two sticks installed on a temporary basis as specified but the task was cumbersome with lots of filing to get everything to fit together. Here is where I am tonight: are not my control sticks grips cute?