Insert another row underneath the headers and merge several cells.
Add text to instruct your users to click on the cell.
Format the cell so it is noticeable
Link the text to your custom map.
Freeze the top two rows.
Attributions
"Happy Alley by Kevin MacLeod" by incompetech.com (http://incompetech.com/music/royalty-free/index.html?isrc=USUAN1100482) -- Licensed under Creative Commons: By Attribution 3.0 License (http://creativecommons.org/licenses/by/3.0/)