Transmit Variables from Storyline to the Player/SDK

Hi all!  

I'm using the Storyline SDK to customize the player frame.  One goal is to make the 'Next' button only appear when the Designer (person creating the page/slide in Storyline) wants it to appear.  I've successfully gotten the 'Next' button to only appear at the end of the current slide's timeline, but this doesn't work for those slides with interactions.  The 'Next' button will still appear at the end of the slide's timeline even if there's a custom interaction (through triggers) on the page that require the Learner to complete them before the 'Next' button will progress to the next slide.

Soooo, it would be great if I could have a Trigger on the slide call some JavaScript that transmits a variable to the player frame.  Once the player frame (the SDK) has the variable, then I can show the 'Next' button.  OR, I could retrieve Storyline variables through the player frame (the SDK).  That way I could simply use a Trigger on the slide to set a variable to TRUE, and the SDK would be set up to frequently retrieve the value of that variable and show the 'Next' button if the variable is TRUE and hide it if the variable is FALSE.

But, for the life of me I can't figure out how to communicate variables/functions between Storyline and the player.

Sorry if this topic has come up before somewhere else.  I've searched and searched and haven't been able to come up with a solution yet.

Thank you very much!