There are couple of things that need to be done.
First override the behavior of custom attributes in the VM template to switch from an input box to a textarea.
Next add JavaScript to control input into the textarea (custom attribute).
Thanks so much for the response!
I kind of get where you're coming from, but if it's not too much trouble, would you be able to quickly explain just a bit further what you've outlined?
I've searched high and low for where exactly to override the behaviour of the custom attributes, but every modification doesn't really make an effect.
This would be greatly appreciated. Cheers!