Here's the update! With a helpful suggestion from R0J0hound to work around a schoolboy error on my part- I now have the facility to both load and save the layouts via JSON.
At the moment it's a simple 2 dimensional array, but if I can get it working correctly, there's no reason a 3rd can't be added, and perhaps using a string instead of a number, can assign several properties at once to the different blocks.
Ideally I'd love for the editor to open the url of the game and launch it, but that may be a bit ahead of me as it'll mean sending variables via POST or saving via AJAX, neither of which I've achieved as yet.
Here's a shot of a successfully loaded layout in the editor.
At the moment the "save" button simply triggers a new tab/window with a download link (default Construct 2 Array JSON save behaviour) , which can then be opened in notepad, and pasted back into the text box offered on clicking the "load" button.
I have a couple of problems to work through, if anyone has any suggestions.
1: The textbox, once triggered, keeps focus even after clicking elsewhere on the canvas, meaning the backspace key to clear the layout n edit view no longer works, as the textbox is capturing keystrokes.
Is there a way to turn off focus for a text box, or should I instead destroy it and create it each time?
2: Can anyone remember the plugin for saving out cropped .png images from contsruct? My ultimate plan is to allow users to save a name + thumbnail image to be loaded at runtime from a second CSV/JSON file listing the user created designs.