Select a Specific New Blog Template Using Gravity Forms

I've created a form to sign up to my Multisite using Gravity Forms (+User Registration add on) and I would like it to automatically pick a specific one of my New Blog Templates (made using the New Blog Templates plugin).
I know you can show all of the templates using the standard method included, but I would like to be able to pick for my customers, 1 per form.
There is mention of a method of achieving this in this post:
But it does not seem to work any more.
Alternatively a method of only showing a particular category of NBTs would work great for me.