Forcing Alternate Devices for Traffic

Hello,
I'm seeking to use webbot to retrieve information and not use the default device
that it would be assigned by the routing table.
I believe this is possible, ping, for instance, can take a -I argument to force
it to work out of a specific device.

So far it seems as though this would require modification to both the webbot
program, and also to the libwww library itself, perhaps modifying the format of
a request object to contain device selection information.

Does this seem feasible?  Has anyone heard of such a thing being done before? 
Is there another method of doing this that is easier?

I appreciate any input.  Thanks,
 - David Moore
Grad student at Notre Dame.