I don't use a controller, but if I'm reading Fleur's suggestion correctly, the idea is that you don't continually switch targets while applying DoTs, and neither do you use assist macros that would depend on the friendly target staying on one mob.
It sounds like the way I do it with a keyboard: assist the MT for its initial target; switch to that target and DoT+Bane (while forcing Embraces on the MT); can now assist the mob to retarget a tank if you desire, or continue DPSing if direct healing not required. The tank can target whatever it likes at any point since you aren't depending on an assist macro to apply DoTs to enemies while hard-targeting the tank.