Hey ZeoZen,
I don´t know if I am a stupid to comment on your solution that you have posted in 2015 but it would really help me with my project.
Your suggestion seems pretty convincing but would really appreciate if you could explain it with some screenshot or simple drawing for those who have problems with Vectors.
PS: I am working with the mannequinn of ue4 in a irregular terrain and I need the foot to be placed correctly according to nature of ground where the character is stepping.
Thank you so much for understanding!