There is something out there, context aware resizing, don't know if you will be able to use it, but it's worth looking at, that's for sure
A nice video demo (Enlarging appears towards the middle) http://www.youtube.com/watch?v=vIFCV2spKtg
Here there could be some code. http://www.semanticmetadata.net/2007/08/30/content-aware-image-resizing-gpl-implementation/
Was that overkill? Maybe there are some easy filters you can apply to an enlarged image to blur the pixels a bit, you could look into that.