Building a rig for litecoin mining here and have had to sort through the misleading information posted but never deleted.

So regarding dummy plugs. They are not needed. This works I've tried it on three different computers.

I utilized MSI afterburner and used the unofficial over clocking configuration (I'm not over clocking just using the specified clocks). I have MSI Afterburner load at start up and basically write the clock speeds to the cards. When windows boots up the cards that are not attached to monitors are disabled (a microsoft feature). This process of writing of the clock speeds to the cards by afterburner enables access to the cards. It does not work unless the overclocking configuration is enabled.



Please note that the unofficial over clocking configuration is as follows:

1- Change security settings on MSIAfterburner.cfg most likely located in c:\Program Files (x86)\MSI Afterburner to allow editing of the file if required.
2-  Make these changes

UnofficialOverclockingEULA   = I confirm that I am aware of unofficial overclocking limitations and fully understand that MSI will not provide me any support on it
UnofficialOverclockingMode   = 1

Afterwards when you open Afterburner configure it to load with windows (for automated mining) and apply over clocking at system startup. As I said earlier I don't actually over clock I'm just writing the normal clock to each of my cards. This enables them and they no longer need dummy plugs. Also save a profile it comes in handy to re-enable a failed card when experimenting with different configurations.