My Hyper-V Server 2008 R2 box has 2 partitions, one for the OS and a second for data. Can I configure my guest virtual machines to have access to that data partition? Preferably so that the guest OS sees it as a physical drive, not a mounted network share.
No.
You can assign DRIVES (Physical) to machiens a drives, but not partitions.
You can create a "fixed" VHD that fills the entire volume. Then you can assign that to the VM. This will have the exact same behavior as passing the partition through to a VM.