There is a flag in the export settings for FBX to export “Only deform bones” in the armatures tab of Blender (2.76b) as well. But you have to switch this deform flag for every bone off and on manually (actually it would be easier if this would be done via some weight-check I guess). I’ve removed the deform flag for my own IK bones and it’s poles and it looks like it should in UE4 (only deform bones and the armature called “root”).