It should be possible, but a bit complicated.
You could use hoverpopups from links like item 1 here:-
The popups normally show in the same relationship to the link, so if one link is 35px below the first, the popup will be 35px below the first, but by giving each popup a class with different offsets from the link you can position them where you want.
You then code the Google map and code the class positions for the hover popups to show a small icon like a pointer or text in selected positions over it.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.