Route specific ports through isp gateway instead of vpn

Hey everyone, I've been reading a lot on these forums but I'm still quite confused. I have a tomato install with a connection to openvpn. One of my roommates wants to use steam for games but steam blocks users who use vpns. How would I go about setting traffic intended for specific tcp and udp ports (ports steam uses) to my isp gateway instead of the vpn. I want to try and set things up to where everything goes through the vpn on my network except steam traffic. Your help would be extremely appreciated.

Here are the specific ports:
Steam Client

  • UDP 27000 to 27015 inclusive (Game client traffic)
  • UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
  • TCP 27014 to 27050 inclusive (Steam downloads)
  • UDP 4380

Dedicated or Listen Servers

  • TCP 27015 (SRCDS Rcon port)

Steamworks P2P Networking and Steam Voice Chat

  • UDP 3478 (Outbound)
  • UDP 4379 (Outbound)
  • UDP 4380 (Outbound)