I made one for my bike, then one winter I made a few sets and sold them. With your skill/tools you won't have any trouble making one.
I used a BMX left brake lever, the stock clamp size is 7/8" for my clip-ons, and I bored the clamp out to 1" for the stock bars. I had to lengthen the decompression lever on the head to allow more travel and leverage. I also had to modify the cable mount on the head to match the longer lever. I bought stainless bicycle cable inner/outer to make the longer cable, and machined brass ends to solder to the cable. The only really tricky part was learning how to solder to the Teflon coated stainless cable - you need to sand/scrape the cable end to get the Teflon off, then put some liquid acid flux on the cable end. Then....the cable is so small it is easy to overheat it while trying to use a torch - it is much easier to use a small piece of steel clamped in a vice, and melt the solder on the steel and dip the cable end in the molten solder to tin it. Once that is done it is easy to heat the cable and brass fitting to solder them together.
Here is the text/photos copied from my Bike Build.
I went to the local bicycle store and bought a left brake lever for a BMX bike. The length of pull is far more than the compression release and I was worried about being strong enough to pull the lever....or breaking the cable.....so I made a longer decompression lever that would match the distance between the pivot point and cable on the lever. I had to make a new mount that would put the cable in line with the new lever. The new parts are painted black.
I then mounted them on the engine and I use a bicycle brake cable that I cut to length and soldered on a proper end fitting.
I then mounted the new bicycle brake lever on my clip ons. I had to angle the lever up a bit - so it did not hit the passing light switch when I pulled it in.
It seems to work proper now. I have enough leverage to pull the exhaust valves open with my fingers.
With your skill/tools you won't have any trouble making one.