I have never seen a missed approach procedure, where you have to maintain a DA/DH or MDA?
Are you referring to the high level go around? If so there are 2 ways of doing it.
As has been mentioned, you can simply select TOGA, which will activate the GA mode then pop the thrust levers quickly back into the CLB detent. The only problem with this is it is easy to bust the GA altitude if you are close to it in the first place, and possibly exceed VFE. The procedure we use in the ailrine I fly for, is to push VS, which will maintain your current altitude and call go around flap (retract one stage). Once you have established level flight raise the gear, and use VS to climb or desend to you GA altitude, then using selected speed to accelerate and clean up. You can also pull for heading to disengage LOC mode, then push for NAV to fly the lateral profile of the GA procdure.