Define custom navigation paths in Google Maps

Question

I am trying to implement something like Google's indoor maps feature, locally in my iOS app, using GroundOverlays. I could easily get the overlay part done by overlaying a .png image at some position in the map, using the API. I could also implement a custom floors switcher, just like Google's one, so it changes the floor overlay image. However, I still miss the ability to navigate in the native indoor maps. How can I define custom navigation paths in that region so when user navigates between two points inside it, the calculated path gets generated with respecting them?