Actiontext used for templates/placeholders

I've got a little business finance management app and I'd love my users to be able to create their own custom templates for quotes/invoices. The way all my competitors do it is through merge fields with DOCX templates which is fiddly for the user.

I just watched Chris' railsconf talk on action text and creating custom attachments and was wondering whether instead of attaching a record you could leave a placeholder where i could pass the record in via json and it renders in the template? I've only seen examples where an actual record is retrieved so wondering if this can be done? Alternatively would the better way be to use a normal wysiwyg editor and create a placeholder for the record attributes that gets populated? Keen for all the ideas!