Certain tasks are performed with the kind of infrequency that ensures you have to spend 10 minutes googling how to do it, every time you need to do it. In my case the conversion of sparse, compressed VMDKs is one such task so I thought I would document it here for my benefit (as well as others).
A number of forensic tools will handle a flat VMDK but refuse a sparse/compressed one and as such when receiving VMDKs provided by clients this can be an issue. There are a few ways to perform this conversion however as I have VirtualBox installed on most of my PCs I tend to use the associated VBoxManage.
The command below will read a source VMDK and create an output VMDK which is not sparse/compressed:
VBoxManage.exe clonehd [source VMDK] [output VMDK] --format VMDK
Given the default install path of VirtualBox the fuller command below will work:
"C:\Program Files\Oracle\VirtualBox\VBoxManage.exe" clonehd [source VMDK] [output VMDK] --format VMDK