xpro1 lock focus and exposure?.seperately?

my x-t10 has a button i can use for each exposure and focus on the back of the body and i like to make use of them both. On my new xpro1 i notice there is only one button, so it seems an either one or the other or both together on the one button situation. can anyone fill me in on how to lock exposure separately, if i'm just using that back button to focus.? thanks