I know this is an old thread now, but I looked this over before attempting to do this mod and just thought i'd update it with what i did as i think it's a easier and safer option
So I managed to do this without cutting any of the selector shaft off. The gear linkage is hollow, but the clamp had deformed the ends a little making it impossible to push the selector in any further. I simply opened up the clamp on the linkage and the ends of the linkage enough to be able to push the selector further into the linkage.
I'm not sure how much i pushed it in, but the linkage in now almost right to the end of the selector rod and clamped back up, so i don't think i'd be able to push it in any further.
Gearstick position is better, But i think i'm still probably going to get either the scenic mod stick, or a PMS shifter at some point.