Well, as you can see it could be extended about 250 units to the left before the ugly edge pops out, and the whole texture can be scaled, so it's pretty much possible to cover half of your screen. I think it'll look awful, but I'll give it a thought tomorrow
or the day after...
Edit: I've just found the right edge of the background texture in another, unused background widget
Still don't understand why they're splitting these textures, it's not like you can resize one and not the other if you need a different size
So moving the sheet should be possible, with replaced background. Vertically it should not be difficult to resize. Horizontally, that's a different beast, one that's probably not worth the effort.