Putting the light on the handgaurd with a carbine length gas system puts the light to far to the rear for my taste. If that is not a issue for you, then I see no reason not to bolt a piece of rail wherever you want on the handgaurd and call it a day.

I would rather grip the carbine as far out as possible and still be able to adctivate the light. A front sight base mount is one way to do this with a non-railed carbine.

Here is an MI FSB rail holding a G2LED w/ Z49 tail cap taken from this thread: