Scripting is the way to go for this one.
Take a look at the CallbackURL reference page, and in particular, the example at the end. This will show you how to split a draft and call an app like Due.
Next take a look at the Due x-callback-url documentation. In particular, the add option and it’s parameters. There are examples on that page along with thw technical descriptions. This should give you the info you need to replace the Fantastical URL scheme elements in the example referenced above.
That should cover the elements you need to put together your multi-line solution.