How to use a particular interface in net/http


Sorry if this has already been asked but I wasn’t able to find the
response via search.

I’m doing some page scraping for a client and need to connect to their
vpn server. So I have the vpn client running on my linux box, and this
creates a new interface, say ppp0. Now, when I run Mechanize/open-uri,
etc. I need to be able to bind specifically to this particular
interface, because the other interfaces are to the internet in general.
How do I do this?