I've just made some Mother's Day cards which are a bit fat owing to the presence of flowers in a 3D vase on the front. Can anyone give me some tips, or even a template, for making an expanding envelope? The cards are tall slim ones; I can probably find a spare envelope to take apart for a basic template, and add to it - but how? In which direction? Do I insert a gusset (ooh, matron) or put pleats in it?

Help, please!