[emidln]

No, you need to do what anyone who has fringe requirements has to do: patch the library yourself. Modify urllib3's (requests uses this as a go between for httplib/http.client) to accept/pass on the source_address that the HTTPConnection from httplib allows and then modify requests to accept/pass this on. This will take, at first glance, maybe half a day with some tests (likely much faster, but I'll allow that there might be something more involved than modifying urllib3's HttpConnectionPool and the accompanying changes for requests's Request model.