Hi,

Google has no problem with collapsable Div's elements that are crawlable. I mean if the bot can see and read the content in the collapsable div, there is no issue with that. I have used this 100's of times and never had ranking issues + in the text-only version of google cache, i see the whole content.

So, use some css + onclick njs function and u're good to go. Here is a sample hidden content in a collapsabel div , that is totally legimate: derniereminute.net  , you can check this screenshot for more details: http://awesomescreenshot.com/08c2ie9rff

If you need more help, let me know