Required tool: Virtual Disk Manager (vmware-vdiskmanager.exe) that comes with VMWare Fusion and VMWare Workstation or can be downloaded from VMWare KB 1023856 (Attachments section). User guide.
To merge disk execute the following command line:
"C:\Program Files (x86)\VMware\VMware Workstation\vmware-vdiskmanager.exe" -r <path_to_source_vmdk_disk> -t 0 <path_to_target_vmdk_disk>
Dev Tips & Tricks 