The beta is now available if you login to your account on this site (2.38.1 beta). You need to know your map’s name (see the FAQ for how to assign a name). Assuming the name is ‘mymap’ you can use javascript to get the infoWindow handle:
mymap.getInfoWindow();
With the handle you can use google’s “domready” event to detect when the window is open.
By the way, you could probably also just embed an ‘onclick’ event in the link. It’s a little uglier but it would let you avoid getting the handle, etc.