Corresponding pictures from the iFixit framework 16 review:
Not quite as clear as the closeups in the FW13 video, but it seems like there are two places where extra millimeters might be added, marked with the red arrows, and in fact it might be possible just to put a flat shim underneath the hinge at the location of the blue arrow which would be Very Easy Indeed if true.
EDIT: the hinges are already in the Framework store: Framework – nice pictures there; I’m hoping I’m right about a flat spacer being all that’s required. They are/will be also selling the midplate for $99 which would one way to “mock up the top surface”, although a bit more expensive than a STEP model would be. 
(@nrp if you had an extra refurb or not-consumer-quality midplate lying around, I’d love to borrow it for test fits!)