The production of complex three-dimensional dendritic structures is an important step in the application of semiconductor nanowires. One promising method for achieving this is the sequential seeding of multiple generations of epitaxial nanowires using metal seed particles. However, it is difficult to control and predict the position of second and higher generation nanowires with respect to the first generation. Here we demonstrate a procedure for controlling the position of second-generation epitaxial nanowire branches on vertically aligned nanowire trunks. This method uses a spun-on polymer layer that masks first-generation wires to a specified height, preventing the growth of nanowire branches at lower positions as well as new nanowire growth on the substrate. This method appears not to be dependent on the materials or growth system (in this case MOVPE-grown GaP is demonstrated), and hence is likely to be applicable to a variety of materials systems and growth procedures using metal seed particles.