I don’t know if you’ve tried this but you can export the mannequin from UE4 as an fbx and import it into 3DS Max. The hierarchy remains in tact and ik handlers are included. However, you would have to create your own rig controls and parent them to the joints. In short, it gets you most of the way there but some work will be needed. Considering the large # of 3DS Max users, I’d imagine someone must have already done this.