The unique element ID's are pretty much as advertised. You can't have more than one with the same name in any Hype document.
What I'd probably try doing is setting up a variable at the load of any given layout, something that indicates what the layout's dimension is. Maybe something like
window.thisDimension = '500';
Then, you can name your elements appropriately in the unique element ID fields:
...and so on, placing all the '300' items in the 300-wide layout, the '500's in the 500, etc. To address them, you'd access them as:
'control_' + thisDimension;
...feeding the result into your unique element ID code.
I wonder about the workflow here, though; is there a reason you're not just letting the entire Hype document scale, setting up the various elements to respond with the pinning options in the Metrics inspector?