the "V" cut is done on the inner part or lower part of the shell.
If you pull the liner and look towards the back you will see the part of the cuff that wraps around your foot, then there is a tall part of the lower boot that rises up to about 3/4 of the height of the rear spoiler inside the cuff. This stiffens the forward lean on the boot as well.. On this part that rises up there is a marked "V" as a guideline. You don't have to take it all the way down, Start with about an inch, and keep cutting it out until you get the desired flex..
If I get a chance I'll take a picture of my Wife's boot which has had the "softening V cut out. She is on an Xwave 8 but same idea..
As far as a booster strap, see www.boosterstrap.com