You are not alone in wanting to be able to do that. There is a
mechanism for storing Blob objects into the local server, that can
then be linked to as regular urls, but there is currently no way of
getting a Blob with arbitrary content.
http://code.google.com/p/gears/issues/detail?id=786&q=blob&colspec=Version
Milestone Owner ID Summary Component
This functionality has been requested since at least June last year,
and it looks like the needed code is present in non-release builds -
google has been silent on the matter though. :-(
Cheers,
Len.