Reply to Midi button drop

Hello good people!

I have technics setup running traktor pro 2, what I'm trying to do is map a toggled midi button so that i can start a song exactly on a down beat while the record is already spinning. So basically: the record is spinning on one channel, but the song is not playing, I press a midi button and the song starts exactly on that down beat and then the song will play and I'll be able to use the record normally from then on.

Does anyone know how I should go about mapping that?

Thanks in advance!!