Take a look at TRex Arms' Lucas Botkin's Glock 19 and his use of the Sidecar Holster. You might want to have a custom G19 GBB based on this and get the holster to go with it... "Lucas Botkin runs his EDC Glock 19 and Sidecar holster for 22 minutes running drills and discussing some shooting tips regarding concealment holsters."