Rails admin does not have anything special that can help you with this. The edit view, the closest thing that could help you, is auto-generated from the model fields and associations. And unless you want to add a model for each template you probably should steer clear of this approach.
What you need is to build a custom action. You'd have to practically build everything like a regular controller. Check out the actions page of the rails admin wiki for instructions on how to do this.
Good luck