Yes, it is possible without a mod. You simply have to place a antigrav platform entity underneath the player and use a texture that will make the platform transparent.
http://forum.thegamecreators.com/?m=forum_view&t=153479&b=23
That link will take you to my thread on the topic, which has a tutorial, and my script for the platform. Make sure to put that script in the AI MAIN for the platform.
Seeing my thread is still on the first page, please use the search function next time.
Actually, I browse around the boards just to critique stories to make them more original, it seems that many are doing the "Shoot everyone in your sight"
-Light Samus