Adfs proxy and dmz configuration

You could do what you're trying to do with Squid Cache and the tcp_outgoing_address configuration parameter (which I've used on Windows and works fine) but, as Chopper3 says, it's probably better for you to explain why you're trying to do that instead of just asking for what you want to do.

Edit:

You could use ACLs in Squid to define the particular list of sites that need to be sent out the other tcp_outgoing_address. This is a bit of a heavyweight solution for your own local machine but it's certainly feasible to do.

This isn't necessarily a Server Fault-type question, but it's possible that somebody could want to do something similar in a corporate LAN setting.

I've got a Customer site where, for example, accesses to some web sites through a proxy server need to be stamped with a "special" source IP address (by way of the tcp_outgoing_address directive an an authentication ACL that back-ends to the Active Directory) depending on how the authentication occurs (to allow a rather "dumb" upstream proxy server to know that the user is of a given "class" designation when accessing these web sites).

While different technologies for the front and back end give a nominal increase in security the amount is quite debatable. Put simply, just because the front end is compromised doesn't in and of itself mean the back end or any other art of the network is compromised. Although it can be argued that whatever method was used to compromise the front end can now be implemented on the back end it doesn't necessarily mean that method will be effective against the new target(s).

With that said, if you have pretty much the same systems and configurations for both front and back ends then yes, you do gain extra security by using a different technology for one of them.

Whether you use the same or different technologies, I suggest using different accounts on each system.