Existe um programa chamado ForceBindIP que faz o que você está procurando. Daquela página:
ForceBindIP is a freeware Windows application that will inject itself into another application and alter how certain Windows Sockets calls are made, allowing you to force the other application to use a specific network interface / IP address. This is useful if you are in an environment with multiple interfaces and your application has no such option for binding to a specific interface.
...
Some programs that have been tested to work with ForceBindIP include DC++, uTorrent, Quake II, Quake III, Diablo II, StarCraft, Internet Explorer, Mozilla Firefox, Google Earth, Infantry, Real Player, Unreal Tournament 2004 (requires -i), Outlook 2000 (requires -i). Programs that do not work include GetRight (anti-debugger / forking techniques), WinCVS (forks cvs.exe)
Funciona apenas em sistemas Windows de 32 bits, o que pode ser um problema para você.