The only way I could think of to do this off hand (and I'm not an authority by any stretch), would be to create a VHDX in the share, mount the VHDX, then utilize ODX to copy/move the data into the new VHDX.
Utilizing ODX will leverage native cloning technology in the volume so copy will be very fast, and it will not require space overhead since the files will already be deduplicated.
You could also do it with a LUN since we support NAS to SAN ODX.
The ConvertTo-NcLun and ConvertTo-NcVhdx Cmdlets will allow you to convert your LUN or VHDX back and forth to either format once you get there.
Does your backup application support NDMP? That might be another option to look at.