Is this "any two" or "Displacement and something else"? Displacement is like 0.2s longer than the other GCDs, so it doesn't play well with others even if you have a 20ms ping. Any two oGCDs that do not include Displacement should work together as long as you're not maximizing spell speed for some reason.
And even then, if you like playing RDM but can't fit two oGCDs into one gap, just split them. It's not a big deal unless you're doing speed clears.