You're going to have to tear a decent amount of the bar apart, since the flasher is gong to be located underneath the channel, or upper level, that holds the rotators. Is your MX the kind with a deeper channel in the middle, or is it the kind with the rotators that come through a flat center section? If it's the latter, then there's going to be even more breaking down of the bar.
Once you remove all the appropriate parts, it's simply a matter of installing the flashers where you want them to go, then run the wiring to the flasher like the pair you already have in the bar is wired. It shouldn't be too difficult.