You can style the map with the Google Maps API version 3 by using the parameter stylemap (version => 2.16).
This should be a json variable. You can make it here.
In the overlay Map Style push the button at the bottom JSON and copy this value including [...].

The next example is for setting off the roads:

{mosmap styledmap='[{featureType: "road", stylers: [{ visibility: "off" }]}]'}

Other interesting possibilities:

• To switch off other Point of Interests on your map: [ { featureType: "poi", stylers: [ { visibility: "off" } ] } ]
• To switch off other businesses on your map: [ { featureType: "poi.business", stylers: [ { visibility: "off" } ] } ]