Retevis RB637 PTT Solution needed

Hello guys and girls from the forum! I am fairly new to this forum and also to the whole world of these Radios.

I will come to the point quickly: I have the goal to communicate with others while driving with my motorcycle. I have a SENA 30K so this is not much of a deal, but if I drive with my Brother for example who sits in his car with his wife, I would love to have the ability to talk to him. I bought the RB637 to connect it via Bluetooth with my Sena 30K. It worked perfectly and if I press the PTT button, the sound recorded in my helmet is transmitted. So far so good.

I cant very well have the Radio somewhere on my motorcycle where I can press the PTT Button everytime I want to speak. VOX is also not an option because I want to have the ability to communicate via the normal Sena intercom with other motorcyclists. Is there an option to have a PTT Button, its ok if its wired, hooked up to the RB637? All I have seen the last few days are PTT in combination with Microphones and Headphones, and it is driving me crazy after hours of research. I only need the PTT so that I am able to press it maybe on the handlebar. Because all the sound is in my helmet. If you have any information on something like this, I would highly appreciate it. I searched for so many hours and I got to the point where I got the same sites just because I thought I may have overseen things.

Thanks in advance,