"Funnels" won't work - it's simply spread out again as soon as it gets out the other end.
I *think* the way those cheapo LazerQuest/MegaZone 'clones' you get in stores like Argos simply use a fairly powerful IR bulb/diode and lenses - if you use whichever lens it is that makes the beam focus inwards (cocave,covex - can't remember) you could have something like this:
Code:
>---------- Focal Point
> ---------- !
> ----------
> ----------
>----------
Where the thing with the '>''s is the lens.
That would focus it in towards a certain distance - past the focul point would be "out of range" as the beam would be too weak to set off the sensor due to standard inverse square falloff. Although the beam is of course falling off all the way to the focul point, it is also becomming more concentrated due to the focussing - it would be up to you to get the right emitter and lenses so that the strength stayed fairly consistent (or at least strong enough to trigger your sensor) up to the focul point.
With the right kit you might manage a range of 10 or 20 meters - similar to what you get with those 'clones' anyway.
That's my idea anyway.