Before you begin first set your armature to render in front of other objects. Next go to edit from the top menu and uncheck 'lock object modes'. This will allow you select multiple object modes at one time.
Select only the object you want to paint. This object should be a child of your armature. With the object selected change the mode to weight paint. Then select only the armature. Change the armature mode to pose mode. Select only the object you want to paint again.
The bones will render over any objects and have a black highlighting on the edges. You can press control + select to change the bone selection. Now you can paint the object and change the bones whenever you wish.