One way (without changing any DNN code) would be to use Javascript to add an OnMouseOver event handler to the login module's containing HTML element.  The event handler would fire the click event for the module container's maximize function (part of the VISIBILITY skin object).

Your Javascript will need to either be inline and appear below the rendered code for the login module -or- the code can be anywhere of the page if you set it to fire after the page is completely loaded (see here for one DNN-compatible method: Force Javascript to run After a DotNetNuke page is completely Loaded).
 
-mamlin