I'm not sure why anyone would need dummy plugs on Windows 7...

You need to do 3 steps to configure headless miner on w7:
1) Autlogin: http://pcsupport.about.com/od/windows7/ht/auto-logon-windows-7.htm
2) Add your miner to autostart. Gui-miner allows to specify what miners run on start up, so you only need to add gui-miner shortcut to windows startup. Phoenix miner can be started from .cmd file which would call it with proper args. Ofc, shortcut to .cmd file needs to be added to windows startup.
3) Configure overclocking: seems like GUI-based OC software actually cares about card being plugged to something, but ClockTweak app ( http://bitcointalk.org/index.php?topic=9982 ) is a command line tool and works very nicely from Startup shortcut and can change core clock, memory clock, fan speed etc... for any GPU without a need for dummies - however it costs 0.2BTC - cheaper than making dummy. Note: OC will not work when Remote Desktopping, but works fine from autostart.