We study the formation of GaAs nanowire - graphite nanoplatelet hybrid nanostructures. The quasi van-der-Waals epitaxy was used to grow the vapor-liquid-solid nanowires on a silicon substrate covered by graphite nanoplatelets. We have found that either horizontal or inclined nanowires can form depending on the relative positions of graphite nanoplatelets, as well as on the placement of catalyst nanoparticles. We present the model, which is capable of the description of the experimentally observed scenarios of planar and non-planar NW growth. Both theoretical and experimental studies show that the use of nanoplatelet substrate allows engineering the morphology of planar and inclined nanowires.