no need to cut it all the way like that.
get some sandpaper .. or a dremel with the right attachment and jsut sand out the rounded corners on both sides and a little on the back side. Then use a buffing attachment on your dremel to smooth it out
Profit.
and you dont have a ugly *** cut dock... it looks exactly the same but the 3g fits now
Edit: i guess someone else had the exact same idea as me :P