PlacementTarget

I'm trying to create a PlacementTarget in the sandbox to perform an inventory search:

placementTarget = new PlacementTarget
{
type = PlacementTargetType.Network,
typeSpecified = true,
ID = ??????
},

In production, I'd be targeting the Yahoo! Ad Network. This network doesn't appear to be available int eh sandbox. What is the network ID equivalent to the Yahoo! Ad Network in the sandbox?

Thanks,
- Matt