condition System -> on start of layout
action AJAX -> request project file tag
You need to manually import the file into files folder. It should be a text file that is like....{"c2array":true,"size":[3,3,1],"data":[[["Shovel"],["Chisels"],["Pickaxe"]],[["2.75"],["0.75"],["2.25"]],[[3],[0],[4]]}.
Condition AJAX -> on completed tag
Action Array -> Load AJAX.lastData
That's how I did it in this capx:
dl.dropbox.com/u/27144902/inventory.capx
Although, I'm only able to get this to work by manualy loading file. I believe if you want to dynamically import or export JSON you'll need to experiment with AJAX request and post.