I wasn't able to get mine working from the command-line switch but I have been able to do it just by setting my HTTP_PROXY
environment variable. (Note that case seems to be important). I have a batch file that has a line like this in it:
SET HTTP_PROXY=http://%USER%:%PASSWORD%@%SERVER%:%PORT%
I set the four referenced variables before I get to this line obviously. As an example if my username is "wolfbyte", my password is "secret" and my proxy is called "pigsy" and operates on port 8080:
SET HTTP_PROXY=http://wolfbyte:secret@pigsy:8080
You might want to be careful how you manage that because it stores your password in plain text in the machine's session but I don't think it should be too much of an issue.