Attach Biped Rig on already enveloped character for creating animations?

[Ginev]

I first want to say that i created few running animations for my project for battlefront 2 however the animations itself are total crap.So i found that if you are using biped rig for your character you can make better animation moves.So here is my question:Is it possible somehow to attach such biped rig to my enveloped character so i can control his moves better?And if so how to do it.Step by step tutorial will be the best help.

Just an example for what i am talking about: