Actually thats not a "new method" but rather new possibility to vote. Right after being defeated or wining on user made map, on the "Game Over" screen there should be "Your map rating:" field with + and - where you could optionaly rate the map you've just played (or see your rating if you've already voted). That would help a lot and encourage to voting.
[b][size=140][color=#800000]Check it out:[/color][/size] [url=http://vortexwars.com/forum/viewtopic.php?f=4&t=5117][size=120][color=#0040BF]Custom StandAlone Client for VortexWars! [WiP][/b][/color][/size][/url]