This is only possible with greddy boost controllers that have a slot for a 3.5mm jack in the back
Im running td04 at 1.4 bar with no LSD so traction is a major issue when launching.
I decided i wanted a Greddy remote hi/lo boost button that straps to your steering wheel so that i could launch with 0.6 bar then switch to 1.4 once i have sufficient traction to handle it
After seeing these for £90 and not wanting to spend that much on a button i did a little research and found out that it is possible to do with any stereo ear phones that have a 3.5mm jack on.
1. cut off the ear pieces
2. strip the insulation of the wires and plug the 3.5mm jack into the boost controller
3. in each ear phone wire there are 2 wires, 4 in total. touch together the wires in one ear phone wire, your boost controller should switch to hi boost if on low boost and vice versa, If not try the wire for the other ear. Once you have found which ear wire works you can just rip the other ear wire off.
4. I connected mine to my horn for the time being but the wires can easily be connected to a push to make, release to break button.
Total cost about 50p 
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