Probably the closest you could come would be to actually add new features to the map wherever you drop anchor, using the "Add Stuff to the Map" tool in the Maps tab. That way, you'd end up with whatever bay, cove or Anchorage you happen to be at showing up as a Place that people could search on, browse to, or write blog entries for. You still wouldn't be able to simply drop lat/lon into your blog posts, but it would probably get the job done.
I always hate to say "no" to people asking for useful features. But in this case, I'm that I might not be able to help you out. If I knew of another Blog host that had this ability, I'd steer you in the right direction. Unfortunately, every place I can think of will have at least one showstopper issue that would keep you from doing what you're hoping to do.
Good luck, and keep me posted on what you come up with!
Jason