Came looking for a solution for this and was sad to find that there was not really one.
Best idea I have at this time to solve for this would be to embed an iframe (yes, gross but its all I got right now) of a landing page using a custom template from Hubspot on the external page where I want it. I am not really happy with it, but I think it will work.
Our problem was trying to get some targeted marketing (smart content) into our customer base within our application. So we know exactly where we will put the content and how we want to build the layout. I think this will work but I am all ears on if anyone else has had any other ideas or examples of how they have utilized the smart content on external pages or in applications.
If Hubspot wants to keep people within their “CMS” they can still accomplish this request with the use of embeddable smart sections or something like that. Just like a form, allow customers to embed a section of content (including CTA) on an external page. They would create those sections and all that data in the CMS, and just like a form, Hubspot would still be able to collect all the information on that section (views, clicks, etc…). I am not sure what they have to lose by offering this.