How about a separate allergy-friendly menu in your restaurant?
Many customers with food allergies will simply walk away from a business if they can't easily see free-from options on the menu. Instead of losing this business, why don't you create a completely separate menu of options for your food allergic customers?
KISS - 'Keep it Separate. Simple' is the motto behind reducing the risk of a customer having an allergic reaction. So along with keeping your food and utensils separate, create a whole separate menu that you can proudly have on offer. The menu can clearly identify which food items are free from the most common food allergens and outline how you store, prepare and serve these meals separately in your kitchen. Having walked away from many cafes myself, I can assure you that it will full your food allergic customers with relief knowing they are in safe hands. And they will spread the word!