You normally don't have to do anything. What happens behind the scenes is that if you use GET ALL, Adventuron identifies all the objects that are in scope (using is_beside) and attempts to get each of those objects. The action handler for each object is exactly the same as if you had typed them individually. I'd strongly recommend against overriding the default behaviour with :match "TAKE ALL", as this prevents you getting objects that you've dropped that don't have to be bought. If you're having trouble with GET ALL, there may be something wrong with the action handlers for the individual objects. You should check this first.
As an example of how this works in practice, go to the stationery store in 'Igor's Quest' and try GET ALL. You'll get separate messages for each of the objects that needs to be bought. The only downside is that if there is an object that can be taken, I think you get the auto_redescribe and the screen refreshes before you can read all the messages.