No. The hypospermia, dysspermia and hypotestosteronism from mj may or may not be reversible. Nothing will mitigate it while using. May or may not improve on cessation of cannabis. See http://www.Health.Gov.Au/internet/main/publishing.Nsf/content/health-pubs-drug-cannab2-ch65.Htm.
Sorry. Tell him to grow up and quit weed. If he can't then don't have children!