Can't you go Mini-DVI-->DVI and then use http://www.monoprice.com/products/p...=10246&cs_id=1024604&p_id=5998&seq=1&format=2 to change that to Male MiniDisplayPort?
They have other lengths (6, 10, 15ft), I just clicked the 3ft one first...
Edit, shoot...I just realized they're all out of stock/on BackOrder, but maybe they'll be in shortly? =\
This wouldn't work because the ACD has a male MDP plug. You'd end up with two male MDP plugs and no way to connect them. What you'd need to do what the OP wants to do is Mini-DVI to Female MDP, which doesn't currently exist AFAIK.
So what exactly is the port on the ACD itself? It's not the same as the port on the side of the UMB and UMBP models? I thought the plug going in to the ACD was a male cable plug and the female receptacle was on the monitor?
If somebody could take a pic of ports ON the ACD, that would be great...
There aren't any. The MDP, USB audio, and MagSafe are all part of one cable that connects directly below the power supply. The only other ports are 3 downstream USB ports.