There is a significant interest in the production of vibrationally excited H2 molecules because of their application to H- volume-plasma sources, plasma chemistry etc. We consider the vibrational kinetics in a hydrogen flow, which passes through a channel, the H2 molecules being previously excited in a hydrogen discharge. It is shown that an essential increase of the population of high H2 vibrational levels may be achieved in the hydrogen flow by means of a proper choice of channel wall material and by the appropriate organization of the flow. As a result, the significant enhancement of the effective rate constant of volume-plasma H- generation due to the dissociative attachment may be achieved. The effect depends only upon the mean H2 vibrational energy in the inlet of the channel.