In this work, we propose using the low defect density wing region arising from epitaxial lateral overgrowth (ELO) for the development of Group III-nitride flip-chip vertical-cavity surface emitting lasers (VCSELs). The ELO wing is intended to be incorporated within the VCSEL cavity, supporting the n-side distributed Bragg reflector (DBR) mirror, and must therefore be very smooth. We measure the surface morphology of the interface surface of the ELO material after separation from the growth substrate, finding that the interface roughness changes with the composition and thickness of the ELO mask. Sub-nanometer surface roughness suitable for the placement of the DBR mirror is achieved using mask layers terminating in Si3N4, or via 300 nm thick sputtered SiO2.