Yes this is possible without problems. Have a look at the image.ini. This hsows you how to set up an alias for your thumbs. Then wherever you display an image using attribute_view_gui in your templates, use image_class=thumb as additional parameter.
You can also check here, although I am not sure whether everything is still correct here: http://ez.no/download/ez_publish/changelogs/ez_publish_3_3/new_image_system
