First create a normal Mac OS X 10.8 64-bit Virtual Machine without installing the OS.
Then use "/Applications/VMware Fusion.app/Contents/Library/vmware-rawdiskCreator" to create a meta-data .vmdk (virtual hard disk) pointing to the external hard drive.
Then manually swap out the empty virtual hard disk in the Mac OS X 10.8 64-bit Virtual Machine created earlier for the one created with vmware-rawdiskCreator and edit the .vmx configuration file to reflect the change.
Also while editing the .vmx configuration file add the following option to it as well.
suspend.disabled = "TRUE"
Also note that in addition to not suspending, which the above option does, one also should not take Snapshots (or use AutoProtect) with physical disks! 
unknown20c9d045826f:Library mike$ sudo vmware-rawdiskCreator create "/dev/disk3" "1" "~/Documents/Virtual\ Machines/My\ Raw\ Disk" lsilogic
Unable to copy the source files to the destination files.
unknown20c9d045826f:Library mike$
Either quote an argument that has spaces in it or escape it with a backslash but not both.
Whenever possible I like to subscribe to the KISS (Keep It Simple Stupid) method of doing things!
I just tested this using a USB Flash Drive that has OS X 10.8 installed on it and here is what I did.
Created an empty "Mac OS X 10.8 64-bit" Virtual Machine and then closed VMware Fusion.
The USB Flash Drive is "/dev/disk2" at the moment as I have another external device using "/dev/disk1" and "/dev/disk0" is the internal SSD.
Since I use several programs on a regular basis found in "/Applications/VMware Fusion.app/Contents/Library/" it is in my $PATH so I do not need to type other then the programs name in the Terminal.
So I open Terminal and it's opens to my Home Directory and I issue the following command, as is and without quoting any of the arguments as it's not necessary unless <virtDiskPath> has spaces in it or escape it with backslashes:
vmware-rawdiskCreator create /dev/disk2 fullDevice HFSPlus lsilogic
Also note that I use fullDevice not <partNums> in the command line.
This creates an individual file named "HFSPlus.vmdk" in my Home Directory which I moved into the "Mac OS X 10.8 64-bit.vmwarevm" Virtual Machine Package via Finder. (BTW The name HFSPlus was arbitrary as it's formatted HFS+ and had to use something for the example/test.)
I open the "Mac OS X 10.8 64-bit.vmx" configuration file in TextEdit.app and change scsi0:0.fileName = "Virtual Disk.vmdk" to scsi0:0.fileName = "HFSPlus.vmdk" and add scsi0:0.deviceType = "rawDisk" and suspend.disabled = "TRUE" to the .vmx file while I'm at it. (Forgot to mention "rawDisk" option, sorry.) I save the .vmx file.
Next I started VMware Fusion and selected the "Mac OS X 10.8 64-bit" Virtual Machine in the Library and clicked the "Start Up" button.
It booted the USB Device as a "rawDisk" just fine in the Virtual Machine and I see no reason why this cannot also be done with Mac OS X 10.9.