First, you have to open both WVW skeleton and the skeleton you want to make compatible with Working Visible Weapon in NifSkope.

In WvW skeleton
Go to Root->COM->Pelvis->RLeg_Thigh-> WeaponPistol
Highlight WeaponPistol then :
Left Clic->Block->Copy
or
Ctrl+Shift+C

In your Skeleton
Go to Root->COM->Pelvis->RLeg_Thigh
Highlight RLeg_Thigh then:
Left Clic->Block->Paste

Repeat these steps for all the following bones :
Under Pelvis, copy/paste: 

WeaponPistolUp
WeaponMelee1H
WeaponPistolLeft
WeaponRifleFront
WeaponGrenade

Under Chest, copy/paste: 

WeaponHeavyGun
WeaponMelee2HBP
WeaponRifle
WeaponMelee2H
WeaponRifleBP
WeaponRifleSide
WeaponRifleRight

If everything is good, you should count 13 new bones in your skeleton.