Hello Jonathan,
Something that would work with your use case is to use the ‘Add Freetext’ option within your message. Using your missing customer information email above as an example, replace the INSERT REQUEST HERE text with the Add Freetext option displayed in the toolbar within the Content section of the message (to the left of the language drop down menu that currently displays English).
Once the message is saved it can then be used with the Messaging Widget on a page. When the message is selected to be sent via the widget, a free type box is displayed to the user asking them to add their own text, this text is then added to the message wherever the Add Freetext option has been added when it’s sent