All linux LIVE CD or USB flash drive with they access at esxi file system , you have permission to use FASTSCP or WINSCP for copy the wmdk file.
If you have WMFS-5 or WMFS-3 file system depend from your installation. Which file system you have installed?
Choose livecd or usb linux embedded installed with your file system feutures (vmfs5 o wmfs3, add feutures if your linux embedded choosed is supported) in your server and then use tools for copy your file.
Second possibility. Install esxi5 on usb bootable and you must explore the datastore with your .vmdk file, add second datastore and copy file from storage1 to storage2.
Installing ESXi 5.0 on a supported USB flash drive or SD flash card:http://kb.vmware.com/kb/2004784