It's already possible to do that with a workaround. You can map keyboard shortcuts to a switch/button on your transmitter using a software such as this:
Windows: http://joytokey.net/en/
Linux: http://www.lgdb.org/tool/antimicro
Mac: http://alternativeto.net/software/joytokey/?platform=mac
(Keyboard shortcut to start/stop/restart timed race is "t")