Not sure if this is what you're looking for - I can't find any reference to bulk_action online. Bulk actions were introduced in Django 1.1 (see the release notes), so I guess you're referring to removing bulk actions for certain models' admin pages.
If you want no bulk actions available for a given ModelAdmin, simply set ModelAdmin.actions to None:
class MyModelAdmin(admin.ModelAdmin):
actions = None
from the docs.
I don't think this method will remove the checkboxes, or make the listings page look like Django 1.02, it'll just remove the list of bulk actions from the dropdown.