You would have to re-animate the current model.
Since X file format imports animation keys every frame. It is easier to import the x file of the model you want into a model program(Milkshape, Blender, Max, Fragmotion) and attach a new biped and recreate the animation yourself.
If you open up the FPE file and scroll down to the bottom, you can see the animation frames listed per anim. At that point you need to look at the mainAI script and destroy script listed and see how they flows.
These two script can be customized to your animation and make the model do what you want. (test a lot)
So No, There is not an easy way to do this. It took me 4 -5 days to get my first custom one done.
Nothing but coffee in my veins
