Like ibglowin said, you don't need to top off until AFTER secondary is finished.
I have seen others leave out some of the water.
Of course the kit manufacturers do not recommend that you leave out any amount of water when building the kit. Yes, it will make a thicker wine, but things like acid/PH can be out of balance with the alcohol level.
It is an interesting experiment, though.
Regardless, let us know how these short kits come out in the long run.