I did this in my 2003 SANTE shortly after I got it. It's aggravating to do but there's not really anything to mess up. Just don't go through the fiberglass towards the walk through. It's MESSY. Ton's of foam everywhere. We used one of these
http://www.homedepot.com/p/Dremel-Mu...0-04/206360248 (not that brand though) with the flat saw on it. It wasn't hard to do. I took some of that grey boat carpet (I think I got it from nautiqueparts.com)and glued it in to cover up the mess but once I put the V shaped sac up there you can't even tell anything is different.
I ran the overflow from the belly tank into V shaped sac under the seats. Then ran another hose from the top of that sac on the Starboard (driver) side to the original overflow from the belly. This works okay but it's not nearly as good as having it's own pump plumbed in. Once it starts to overflow out the side I stick a 30 cent cork (like a wine cork but bigger) from Home depot in the hole and let it fill the rest of the way up until it lifts the seat a little. (it won't completely fill under the seats theres not enough room). Then I close the valve for the belly. If you don't close the valve to let water in the belly tank on my boat it will eventually drain completely empty while you are riding.
Hope that helps. I don't check this often but my name on planetnautique is gdhall. I think that adding the V sack up front is necessary IF you have 750s or the equivalent on each side of the motor. If I'm learning a new trick and want to ride slow I'll only put about half the water in the 750s and leave the belly and front empty and ride around 18-20 MPH at at 60-65 ft rope. This is a whole lot less painful that riding full speed and since I have to go to work the next day it's better for me.
One last thing, I have 100lbs of lead (200lbs total) (flat tractor weights) under the V shaped sac on each side in the nose.