Using Large Thumbnails

[Andrija Peruničić <perunicic gmail com>]

I understand from the Thumbnail Standard
http://jens.triq.net/thumbnail-spec/ that thumbnails are created in the
normal (128px) and large (256px) varieties.

Stting key /apps/nautilus/icon_view/thumbnail_size to something higher
than 128 in gconf-editor only scales up the normal sized thumbnails
already created, and if there are no thumbnails available the new ones
created are also normal sized. 

1) Is there any way to choose large thumbnail creation by default? 

2) Otherwise, is there a command I can call that will choose the correct
thumbnailer application for a particular file (in order to make a
script)? Finally, in this case, how can I force Nautilus to load the
newly (and manually) created large thumbs?

Thanks ahead!