Adding Blackberries Or Elderberrries To a Stout Kit

[Jazz]

I've noticed quite a few of you make a 'berry stout'. Quite keen on doing the same but adding Blackberries or Elderberries to a regular single can stout kit

I wonder how you would do it ? Would you just soak the berries and use the water or would you need to juice them ? What quantity for 5 gallons ?

Cheers

Jazz