How to clone an MTPFS partition of a mounted Android phone?

Using mtpfs I've mounted a Samsung Galaxy S5 and I need to make an image of its root partition. I want to use dd or the like, but nothing seems to be able to detect/reference an MTP and/or FUSE partition, whether it be mounted or not. But there's no apparent way to do this. How do I reference an mtpfs partition to clone it, and create an image I can mount as ext2 for example? I am using Mint 17.1 and the device is a Lolipop Android OS. Ultimately I need to run data recovery tools on the partition, so I need to copy the "empty" segments of the FAT more than the populated areas.