You're going to have to use the exact same skeleton as the waw body's to rig it, otherwise when you play an anim on it it will deform the character because the joints get 'repositioned'.

So you take a rig from a existing mp-body or zombie ( depending on if its going to be a player model or a zombie ), and then come's the hard part. Binding skin and painting weihgts. I cant really explain that, have little experience with it, maybe try asking whippytrout for example, believe he's done quite a lot of models himself

EDIT:
Look here, at rdvlpr's first post. Give's you an option to have maya do the binds, depending on the model that might do the trick.
https://ugx-mods.com/forum/index.php/topic,5060.msg56524.html#msg56524

Using tomxmodelutil ... Export a player model ...Export your model.
open player model in maya. Delete player model meshes. Drag custom model onto the player model joints. Rotate legs and shoulders joints to fit. Ideally the joints will fit/rotate perfectly inside the mesh.
Select all joints from window...outliner or window...hypergraph hierarchy except these
Tag origin
Tag sync
Tag eye
tag weapon left
tag weapon right
Tag weapon chest
Tag inhand
Then select your mesh and press bind ... smooth bind. Mayas smooth bind algorithm works 99% of the time but sometimes you will need to manually paint a joint or you might prefer doing it manually.
select all joints/meshes and export to xmodel.
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Using the bin/maya/roebuck maya file as a template is easier because it has a test anim setup already. If it looks good on the roebuck skelton it will look good ingame. To use  it Load roebuck file in maya. Window ...outliner ...show all. Select the tag origin then on the right in the attribute editor click "enable override" to show the joints.
You will need to select only the waw joints (they are grouped) if you want to use the roebuck skelton because it has all the joints for every cod character. Once you bind your character Press play to see the test anim.