I've two interfaces: eth0 and wlan0 on a notebook.

Possible use cases:

• eth0 grants me Internet access, and wlan0 is currently connected to a router which does not have Internet-connectivity. For development purposes, I need to connect to the wlan0 by default, but use eth0 for surfing
• eth0 and wlan0 are both connected to the Internet. For a torrent application, eth0 should be used for speed, but for portability of the notebook, SSH should have a connection over wlan0
• eth0 is a wire connection, wlan0 is a wireless one. Sensible data should be transferred over eth0, but other traffic can go over wlan0 as well.

Is there a way to force applications (like nc.traditional or firefox) to use a certain network interface? A wrapper like example-wrapper eth0 program is fine too if such program exist. It would be nice if it could configured within Firefox (in runtime). I'd like to avoid IPTables solutions if possible.