how about 9patch from android ?
can it be used to stretch images ?
maybe there could be few settings affecting small and big tile as well:
Icon Settings
1. Center the specified icon [Browse: ...] and use background [Select color: ...] or fill the background with the color of pixel on position (1,1) or whatever (just to pick up bg color) (see that there are many metro-like icon packs that have solid background, so as not to ruin the concept of clean user modded interface You could consider adding this option as well.
2. Fill the tile without changing the aspect ratio, Choose alignment [top,center,bottom,manual](manual = moving manually on the tile preview by mouse)
How about making the editing process a bit more live ? I mean generating preview tile with
-editable name with checkbox near to toggle it's visibility
-clickable icon
-clickable background or a ribbon looking out behind the preview tile to activate color selection
-both big and small tile visible or a toggle to switch between them
Edit: i had just made a concept art
For illustration look in the attachment
I just fell in love with this app and want to make it perfect(er)
P.S. Please consider in future making the app no higher than 600px coz netbook users, like me can't see the full tile preview
Thanx in advance