Allow block content to be sorted by custom field

[gbstn10]

At the moment the Pages blocks can only be sorted by title, publish date, comments, last post, et cetera. I would like to be able to sort a block based on one of the custom fields in its database. Is there a way to do this now? It doesn't look like there's an option around the default settings.

Is it possible to add this, if there's no way around doing it now?