How do I config a dedicated proxy for accessing unblocked sites ?

[louietan]

Due to the policy of my employer, computers aren't allowed to access the Internet directly but through proxies setup by the IT department, normally we use the proxy server deployed in the US, when we're going to browse domestic sites we switch to the proxy deployed locally.

If I'm not mistaken, the way cow currently works is to only use configured parent proxies when direct access fails, is there any way to config cow to not try direct access by default, but use a dedicated proxy instead ?