Hi Olly,
We have a –Add Textbox to item– function on the site so people can enter special instructions.
When this comes through in the email what ever they have written is displayed under the item like an ingredient.
This leaves it open to people trying to get free paid ingredients by entering the paid ingredient into the text box.
Example

In this example pepsi was written in the text box but it looks like it was a selected ingredient.
Hope that makes sense.