I disagree on adding ice at any time, as would any fisheries biologist that I've ever spoken with about it, and I've talked with a lot of them through the years in my other career; couple that with having a degree in fisheries biology (but not using said degree) and you get where my standpoint is. The differential between the water temps with iced water is often too great and shocks fish almost always. As a result they end up with lactic acid build up, and delayed mortality as a result.
In terms of other additives, think about it this way- the number of things that biologists can use, in terms of chemicals, for fish is extremely limited. Primarily because there is a long term half life that cannot be metabolized by the fish. There are also a large number of the chemicals on the market that will initially strip the slime coat because of the way it acts as a disinfectant. SDSU fisheries dept has done much research on the subject and it's mostly readily available on their pages.
Todd, you make a valid point, yet typically, osmotic imbalance is unlikely to occur in livewell situation with fresh water flowing through. It's almost impossible for that to occur because of the nature of their regulation. To say that an imbalance would occur because of a lack of solutes in a body of water isn't very accurate. What, actually, can occur from a higher than normal concentration of salts, as in the case you present to create a base of .5% salt solution, is that they can actually become lethargic and the salt will then act as a sort of anesthetic.
Where a salt solution is most effective is in long term holding or recovery. There are instances in which it may be beneficial to salt fish in a livewell, but rarely are they effective for the tournament angler, other aspects of the catch/hold/release have much greater effect than salts.
Lastly, define your normal scale for delayed mortality. It's been shown to be in the 25%+ range by some studies (http://www.biol.ttu.edu/faculty/gwilde/Shared%20Documents/Reprints/Tournamentassociatedmortality.pdf) and as high as 51% in others (http://www.tnfish.org/NorrisReservoir_TWRA/files/BassTournamentMortalityGeneGilliland_TWRA.pdf) I have seen studies on the low end around the 13-15% marker, and I've seen studies at near 100% delayed mortality. It's far too subject to specific environmental affects to base a "normal" range. That said, the vast majority of post tournament delayed mortality rates are going to fall below the 20% mark from nearly all modern studies.