Now that I understand what you want to do, I can definitely say…I have no idea. 
I know other users have used QoS (Quality of Service) settings on their routers / gateways (Throttle Bandwidth After Backup Has Started?) or third party apps (see NetLimiter above) that throttle specific traffic or network connections, but I’m betting that @Pectojin will have a thought or two on possibly doing what you’re describing.