Back in stock notification on Shopify POS Terminal

We regularly have customers asking for back in stock notifications in store. We are working with Shopify POS and the POS Terminal as customer display and for card payments.
When we sign a customer up for a back in stock notification we have to put the customer’s email in our POS tablet, which is secured and so we can’t let the customer put the email him/herself. This sometimes causes issues, if we don’t have all the characters correct.

It would be great if the customer could sign up on his / her own by using the POS Terminal touchscreen, as we already use it for email or sms receipts.