This is the easier way to mod this gun. First step as always, take it apart. Lots of screws, keep track of them, don't forget the metal bit on the handle.
Step 1: The Barrel
Inside the barrel you'll find a barrel post. Get some needle nose pliers and twist it out.
Step 2: Restrictor
Here's the part you want to remove. Now instead of un-gluing the barrel or twisting scissors on it, possibly ruining it, just take a drill with a 3/8" bit, and drill it out. Use a good amount of force, be careful as the drill might get stuck on the spring holding the restrictor. Stop every once in a while and clear out the plastic shavings.
Step 3: Reassemble
Put everything back from whence it came. It should fire about 10-15ft further. Watch your eyes!