Variable Slide Size

I'm stumped and I'm hoping the hive mind can help. 

I'm working on a course that's designed primarily for mobile delivery. We're tying to fit all of our content on just a couple of slides, each of which will have a relatively long vertical scroll down the page. The problem is that the slides don't have an equal amount of content on them. So slide 1, for example, only needs to be 1377 px tall, whereas slide 2 needs to be 1700 px tall.

As far as I can tell, the Story Size is a global setting that cannot be overridden elsewhere. If I set the Story Size to 1700, then I'm just going to be stuck with a bunch of empty white space at the bottom of slide 1. And if I set it to 1377, I won't be able to fit all the content for slide 2 onto it.

Any ideas how I could achieve this without using scrolling panels?