Hi Rupert,
You're right - the inner SmartBuilder lesson cannot communicate with the LMS at all (neither are aware of each other).
If the inner lesson is a SmartBuilder lesson, you could instead use local bookmarking ("local storage" - it's similar to a cookie, but a little different). Of course, if the learner starts the lesson on one computer, and switches to another computer, this bookmark will not transfer over. Also, if the learner's browser storage is cleared (or they are using an incognito window), that data will be lost. Our bookmarking template can be modified to store in local storage, or you can build the actions from scratch.
Here's a bunch of info around this -
https://share.smartbuilder.com/public/support/switching-from-SCORM-to-Local-Storage-bookmarking.mp4Let us know if you have any questions!