Gerardo, assuming you know the bounds in which you want to draw a polygon, you may write a script that executes on load, creates a Polygon object, and pushes that to map object.

1.     Get Google map object from Pega AddressMap

var map = $("div").find("[data-test-id='<your test id>']").data('map').getGoogleMap(); //You may write any path but data-test-id configured in design time at control level is preferred

2.     Create a polygon object and add it to map (https://developers.google.com/maps/documentation/javascript/examples/polygon-simple)

// Define the LatLng coordinates for the outer path.

var outerCoords = [ {lat: 54.364, lng: -2.207}, // north west

                         {lat: 55.364, lng: 27.207}, // south west

                         {lat: 45.364, lng: 28.207}, // south east

                         {lat: 44.364, lng: -2.207} // north east ];

    

map.data.add({geometry: new google.maps.Data.Polygon([outerCoords])})