[galaxy-dev] User list and disk space?

Hello I would like to add a column in the admin panel's user list with the sum of the file size of every dataset in each user's histories that don't belong to any ibrary. Is there a way to do that? I had a look at lib/galaxy/web/controller/admin.py and templates/grid_base.mako but I fail to see where the "query" variable (containing the items, therefore the users) come from in the mako template, so I didn't figure out what each column class in admin.py actually manipulates in the get_value() methods. Regards, L-A