MR18 Effects midi map on/off or foot switch?


As a keyboard player who is also running the monitor and FOH mixes.  I'm looking for an easy way to turn the vocal effects OFF while the lead singer is speaking, and ON while he is singing.  Can I map this to a button on my keyboard or to a footswitch somehow?  I see that the MR18 has a midi IN and OUT but I am uncertain how to obtain the desired mapping.