Wuuell, I have overcome the unstable hinge obstacle by using the same mass and inertia for both the axis and hinge body. So the editor pretty much finished.
Here is a short demonstration.
Import a skinned model using the SkinnedModelPipline
Create primitives for the bones, from the root bone outwards
Change the hinge and axis settings for the primitives to make them act naturally
Scale the primitives to fit the model (also, using small primitives causes the entire ragdoll to sometimes go all jittery)
The ragdoll is now done
Ragdoll to model
Model to ragdoll
Ragdolls are saved and loaded as XML files in the output>content>xml directory.
Here is the source if anyone is interested. The important classes are RagdollBlueprint and RagdollInstance in utilities, the rest is required for the editor to work.