Hi Tim,
Question... Does the fuel you are using have ethanol added to it? In some states, this is a common practice.
Rule #9 recommends the use of 92 octane unleaded gasoline; And cites that higher octane fuels may cause higher operating temperatures.
If your fuel has ethanol added, I would tend to think that it would have somewhat of a cooling effect. Detonation is usually caused by high engine temps and/ or improper ignition timing. You may want to check your timing before worrying about additives. Jetting could also be affecting your situation.
As for additives, I know that some of the kart guys, and dirt bike folks, will add a little bit of Marvel Mystery Oil to there fuel to aide lubrication. (About 10 cc per gallon of fuel) That might be of some help to cool the engine temp slightly. My personal opinion is that it's not going to be about fuel additives.
Steve