I think clips are the way forward here. I don't know why Maya needs to lock the anim curves if they come in from a referenced file, it's something that has frustrated me many times.
I think the standard workflow is to have the 'character set' already set up in your original referenced file (saving you time and possible human errors if you have many of the same chars in one scene) this scene would have no animation, just your rigged char in T-pose. Reference from this scene and animate... then create and store those animated clips in your visor. That way if you have a character you need to be repeated in the scene you reference the T-pose guy not the animated file. Drag the clip to the char and offset, lather, rinse, repeat.