bjadams xyboox I used to have similar problem but with Chrome Webstore and future Android publishment.
I'm really sure that actually the best option is to use the Fulscreen Scale mode with additions:
1. Take care about aspect ratios, that can be from 1.33 to 1,5+. You can not avoid to make the background images wider for the 1,5 ratio, and do it in a way it works (not kills the layout).
2. Use Archor behavior - to let some objects float to the left or to the right.
3. Somewhere in your menu/game screen you will need to have a streching area, what is 0% if played in 1.33 ratio and could be up to 13% of the screen width in 1.5 ratio.
My very first game - not an Angry Birds :) - uses this logic:
This not just works on Chrome Webstore, but i have great results in 320x240px, 480x320px and 800x480px screens in Android (not published yet).
If you install it to Chrome, you can adjust the browser window with/height, and it will work from 1.33 to about 1.6 aspect ratio.