Okay here is what I did...
In the Search Community text box (in the upper right hand corner of every page in this Forum) I typed "add raw disk boot camp" (without the quotes) and pressed Enter.
Next I read several posts.
Note: I have a MacBook Pro and it only has one hard disk so I attached a Firewire Drive that has 2 partitions, 1 NTFS and 1 HFS+ in order to process the commands and add a second disk to my Boot Camp partition Virtual Machine. I used System Profiler (/Applications/Utilities/System Profiler) to get the BSD Name of the Firewire Drive as it's needed in the <diskDev> argument of the vmware-rawdiskCreator command.
From what I read I needed to use the vmware-rawdiskCreator command so in a Terminal (/Applications/Utilities/Terminal) I typed the following command:
$ "/Library/Application Support/VMware Fusion/vmware-rawdiskCreator" print /dev/disk2
The output of which was:
Note: I do not store my Normal Fusion Virtual Machine's in the Default Location and the Boot Camp partition Virtual Machine is in a different location then the normal Virtual Machine however I would store the .vmdk files for the 2nd disk in the same location as my normal Virtual Machine and keep a backed up copy prior to use so in the event of having to rebuild the metadata for the Boot Camp partition Virtual Machine. So the <virtDiskPath> argument of the vmware-rawdiskCreator command reflects that.
Next I typed the following command:
$ "/Library/Application Support/VMware Fusion/vmware-rawdiskCreator" create /dev/disk2 1 "/Virtual Machines/BCVM_DISK2/disk2" ide
This created 2 files:
/Virtual Machines/BCVM_DISK2/disk2.vmdk
/Virtual Machines/BCVM_DISK2/disk2-pt.vmdk
I then edited the Boot Camp partition Virtual Machine's Boot Camp partition.vmx configuration file to include the following:
ide0:1.present = "TRUE"
ide0:1.fileName = "/Virtual Machines/BCVM_DISK2/disk2.vmdk"
Note: On my system the Boot Camp partition.vmx file is located at "/Users/WKZ/Library/Application Support/VMware Fusion/Virtual Machines/Boot Camp/%2Fdev%2Fdisk0/Boot Camp partition.vmwarevm/Boot Camp partition.vmx" and I backed it up before editing it.
I then started my Boot Camp partition Virtual Machine and tested Reading/Writing to the newly added 2nd hard disk and all was okay!
Note: To understand about the Virtual Machine Bundle Package and editing the .vmx configuration file have a look at:
A Beginner's Guide to VMware Fusion
Note: For the syntax of the vmware-rawdiskCreator command just execute the command without any arguments.
$ "/Library/Application Support/VMware Fusion/vmware-rawdiskCreator"
The syntax for the create argument of the vmware-rawdiskCreator command is:
"/Library/Application Support/VMware Fusion/vmware-rawdiskCreator" create <diskDev> <partNum> <virtDiskPath> <adapterType>
And you can see what those arguments are from the output of the vmware-rawdiskCreator command executed without any arguments.
HTH