From what I can see there is no breakout of those pins available (maybe I missed them). So you would need to connect to them directly at the BGA.http://jlime.com/mw4/index.php/Accessing_BGA_pins
This type of thing has been brought up a number of times. There are MANY more features on the chip than are broken out even in the "developer" products. Even in the upcoming GuruPlugs (which do better than the SheevaPlug, but are still lacking). Exactly why this is, is not entirely explained (that I have seen), but hopefully future products (and processor offerings) will fix those limitations.