In the same situation looking for something. What about the Akitio node lite:
https://www.akitio.com/expansion/node-lite
And something like one of the following:
http://amfeltec.com/products/pci-express-gen-3-carrier-board-for-4-m-2-ssd-modules/
https://www.supermicro.com/products/accessories/addon/AOC-SLG3-2M2.cfm
http://amfeltec.com/products/pci-express-gen-3-carrier-board-for-2-m-2-ssd-modules/
Seems like this could get the job done, not to portable though. Has anyone tried something like this?