Ask HN: Per application routing on MacOS?

Another HN discussion[0] on VPNs reminded me of a question that has always been nagging at me.

Is it possible to perform routing per application?

For example, if I'm running a VPN service to one of my servers (OpenVPN (Tunnelblick)), how would I route traffic from lets say Firefox through that? This would of course exclude traffic from any other application.