Here's a thought or two for adjustable shelves in that cabinet. Use 1/2" baltic birch panels on either side of the cabinet that you've pre-drilled for the plastic shelf pin brackets. They don't need to cover the entire inner walls, just wide enough to be easily installed, maybe 2" wide. Put two on each side of the cabinet. Paint or stain the panels, if you wish. Use a bead of Liquid Nails to secure these panels to the sides (makes it permanent). Then you can mount a shelf, or shelves, where you've put the holes for the brackets. Granted, you'll loose an inch of width between them, but you'll have your shelf. The thin walls of the cabinets won't support much weight if you try to screw things into them.
Alternatively, if you can drill into the sides without causing major damage, you could make an alignment jig with holes the size and spacing you want (1/4" pegboard?). This would be to drill into the sides for holes to install the plastic shelf pin brackets. This method is used in home kitchen cabinetry. With this, you only need to penetrate the thin wall of the cabinet and not worry about driving a screw into something you don't want to.
Have I done this on my 3670? No, but I've thought about it. With a single door fridge and the pull-out pantry, I haven't needed a shelf in that cabinet by the exhaust vent. At least the wife hasn't told me I needed one...yet.