JetPack subscriptions using Scroll Triggered Box

I use JetPack for my subscriptions and wanted to use Dreamgrow Scroll Triggered Box to get more.
The JetPack info says that I just add “[jetpack_subscription_form]” anywhere on the site and a subscription box will appear. (http://jetpack.me/support/subscriptions/)

However, when I enter this in the Box HTML, the text “[jetpack_subscription_form]” appears instead of the form.

Any ideas how to use this or some other plugin that will let JetPack have a pop-up window once users get part-way down the page.

http://wordpress.org/plugins/dreamgrow-scroll-triggered-box/