I withdraw the question. I found an answer.
Dylan Kuhn answers:
Fortunately it's simple, no custom javascript is needed, just the full post tag:
https://code.google.com/p/wordpress-geo-mashup/wiki/TagReference#Full_Post
If you give me your map tag I can tailor it, but the shortcodes look like
[geo_mashup_map marker_select_info_window="false"]
[geo_mashup_full_post]