The map has quite a few different zoom variations, and an option that could be toggled (to avoid the abuse of spamming in public games), would be for the minimap to zoom into the pinged area to a degree and then zoom back to the orginal size. If multiple pings were made the limit could be to encompass both pings.
Of course the issue would arise if the pings where in far enough locations that the zoom was barely noticeable. If this were to happen, perhaps it's possible to picture in picture the minimap for a brief period of time. The idea's rough, but I'm sure somone who's had experience could flesh it out and make it easy to comprehend with multiple map resizing and merging.
P.S. Another option would be zoom duration, for example 2 seconds between the zoom in and zoom out.