It is possible to do so thought lights only? I know you can use "shadeless" shaders on Superfly but I'd like to keep the existing materials/colors on the figures I want to render. What would be the best aproach to this, if any?

Right, so it sounds like you don't want to use SuperFly. In which case you're using either FireFly or the OpenGL Preview.

Your starting point for a flat light in either would likely be a single Diffuse IBL light, of fairly low intensity (one third or less) and neutral colour, and pointed more or less straight at the character or prop. This should give you a nice flat illumination with minimal shadows.

Firefly render.

Realtime OpenGL render.

With flat lighting you can then also easily get lineart via the real-time Comic Book panel. Render to OpenGL Preview and lay this lineart render on top of your colours render in Photoshop, knock out white - and then they can each be adjusted and filtered without damaging the other layer. You can also render the lineart in Sketch, or render a shadows layer if you don't want to manually paint in shadows.

The shadows on the underside of her glove, and the subtle shadow on her face, are baked in to the color diffuse texture.

Perfect! Thank you very much!