Z3TA+ Arpeggiator Latch question

Hi everyone

I just got Z3TA 2.1 for the Mac and am running it in Ableton Live 8. I would like to press a key on my keyboard and the Arpeggiator to keep running in the classic hold/latch  way, but ik can't find a way to do it. I know you can shift click the ribbin controller, but I would prefer to do it from my midi keyboard. Is this feature missing or can someone tell me how to do it?

Thank you all very much for your help.

Cheers, Blueoysterman