How do I make mapnik to produce meta tiles e.g. 2x2, 4x4 or 8x8 (using generate_tiles.py)

[bongobongo]

I have read many places that mapnik will generate tiles faster if the tile cover a larger map area.
So instead of producing png tiles that are 256x256 pixlels (BASETILE), mapnik can (I believe) produce meta tiles (png) which consist of e.g. 4 (BASETILE's) so the resulting meta tile is 512 x 512 pixels. I have also read many places that instead of generating 2x2 meta tiles, one can produce e.g. 4 x 4 or 8 x 8 meta tiles - which will speed up the generation of the tiles even more.
Would appreciate if someone could explain how this can be done - when using generate_tiles.py, and eventually a modified version of mapnik (if needed). After the generation of the meta tiles, it would be needed to split the meta tiles into "normal" tile size of 256 x 256 png files - with the correct directory structure and file names.