You're correct. There's currently no way to scale photos within Clip but that's a great feature request. We look forward to keep introducing new features in upcoming releases. Amy other ideas you'd like to see in the app?
There was a fantastic feature in Adobe Photoshop Touch (mobile/eol) that would allow you to resize photos back to the library.
The same technology might allow users to scale the image, but not keyframe scale.
I'd put in an early feature request for integration with Project Maestro for controlling scale of images.
Just chipping in here, this is the only element lacking in Adobe Clip that is preventing me from using it. Need to be able to scale photos so they fill the entire screen!