You can do it by specifying the default route to a particular interface from the command line, and then if you want the rest of the software on the system to use a different NIC, then specify local routes with a low metric to the other one.
Here’s the sample syntax:
Assume that you have two NICs on this machine with IP addresses respectively of 192.168.249.105 and 106.
route -p add 0.0.0.0 MASK 0.0.0.0 192.168.249.105 metric 10
route -p add 192.168.249.0 MASK 255.255.255.0 192.168.249.106 metric 5
The -p parameter makes the routes persistent until removed manually – meaning that they’ll survive a reboot.
HOWEVER – do not use the -p value until your testing shows that everything works.
Also – do not forget that the machine has static routes on it, or it WILL come back and bite you in the butt.