Marketpress international shipping - different rates per item

I love how MarketPress gives you options in the Store settings for shipping rates for the US, Alaska & Hawaii, Canada, and International.

I also love how you can add "extra shipping" costs per item.

But we've got a case where a client is shipping different sized items internationally. Some is cheap -- $3 or less. Some is expensive -- $16 or more.

Case 1 - A book costs $4 US, $6 Canada, and $16 international
Case 2 - A keychain costs $1.39 US, $1.49 Canada, and $2.28 international

I can't find a way to make the numbers work for setting shipping rates at the store level. How can we add additional boxes to the individual items page for extra shipping?

Instead of one box for "extra" shipping, can you add the same 4 boxes for Lower 48 States, Alaska/Hawaii, Canada, and International?