I prefer to add my lighting effects in After Effects or Fusion but Moho has some tools for it. For example, something like this is pretty easy to set up in Moho:
For this, I just created a Style that included two Shading effects (one for light and one for shadow), and then keyframed the angle and offset properties. For this example, I set this up as an SBD but to keep it simple, you can keyframe the effect directly on the timeline.
If your lighting and shadow effects need to be more defined and follow the interior of the character (as opposed to just around the edges), you can just draw them as separate layers and use the character's group to mask the lighting layers. Use an appropriate blend mode for each layer (suggest screen for light and multiply for shadow,) and adjust the layer transparency to taste. If the character is moving a lot, bind the lighting layers to the rig (if there is one.)
If you decide to do this in compositing, you can just fill the render as a matte, and then offset two copies to create the light and shadow sides. Add a Blur to the interior edge for softer lighting. Depending on your compositing package, there is probably an effects filter available that lets you do something similar without using mattes, but doing it manually may offer more creative options.
Hope this helps.