I know they're pricey, but I'd just bite the bullet and buy the Wakemakers upgrade bags that are built for the boat.
http://www.wakemakers.com/catalogsearch/result/?q=z1
You could probably sell a couple of those extra bags to offset a lot of the cost, pick up a single WakeMakers 930# bag for the surf side rear/side locker, use a couple of your spare bags in the bow to get the nose down, add some more weight to the bags in your off side ballast to balance and slam the boat some more, and have a pretty damn good wave. I'm planning on upgrading the port side bag in my RZ4 to one of these too since I don't want to risk busting a sack of concrete in my boat or deal with hiding bags of lead shot all over the place.