Spawn props of all the visible body parts. Don't move them. Delete the original human and animal figures. Now assemble them in the hierarchy editor. Parent the animal neck to the human chest. Then the create new figure option should now be available.

Another option which will save time setting up the joint parameters is to export the visible body parts as a single OBJ. Export with the Weld and Body Part Names options selected. Now edit the human CR2 to load this new hybrid.