hacking the mindflex

Hi guys, Im a senior in high school working on my senior project (its a rideable theo jansen strandbeest). Part of my project uses a mindflex duo to control the speed of how fast it will walk. I have tried frontier nerds brain hack with headset only but the could was giving a lot of problems. So I decided to find a new way of hacking it, and since I dont need to read all of the different brain waves I decided to hack the main board in the actual body of the mindlex. What I have right now is Im reading the change in volatage going to the motor that is ment to lift the ball when you concentrate more. But the part im stuck on right now is that with mindflex has a couple of buttons that have to be pressed for the motor to start working so I was wondering if anybody has a good way of pressing the button with an arduino that makes its a non physical button. I've seen a bunch of post online where people suggest using a transistor. I just dont no how exactly I would wire it or what exact transistor I should use? Thanks for any answers

Neat concept but the mindflex could be a dead end:

It would be cool if it worked though!