Hiding Layers When Seek Bar is Enabled

With narrated presentations, I like to throw up the key words as they are spoken, and having them on separate layers works better production-wise compared to trying to cram them into the base layer.  But I want the users to be able to use the seekbar without issues.

For me, an version of Michael Lawrence's solution:  a cue point on the base timeline hiding all layers at the point the last one disappears, and a second doing the same thing at the very beginning of the time line.  Then users can scrub away with no problem... Using the "Group Triggers" feature makes this solution appear neater.

I wish the HTML5 version could instead just "parse" the slide's entire timeline before it decides what should layers should be displayed at any point, but... as long as we can get it to work somehow in the meantime!