Looking at it I only added a single line. generate_tiles.py already checks for blank tiles by comparing the file size of a tile against a hardcoded value. I just addeed a line to delete the blank file.

Index: generate_tiles.py
===================================================================
--- generate_tiles.py (revision 13578)
+++ generate_tiles.py (working copy)
@@ -99,8 +99,9 @@

bytes=os.stat(tile_uri)[6]
empty= ''
- if bytes == 137:
+ if bytes == 360:
empty = " Empty Tile "
+ os.remove(tile_uri)

print name,"[",minZoom,"-",maxZoom,"]: " ,z,x,y,"p:",p0,p1,exi$