Okay so I came up with another way to do it :)
This would be so that you don't have to use a keyer!!
Make a memory that recalls to PGM of the ME. Have the Colour Generator on PGM and set to white. Now set all keys to off air. Now set your Attributes so that you have only Key Active enabled (this way settings and sources are not changed but they are forced off on the recall). Set your PGM bus to Recall but not the PST Bus. Also Disable the changes to the Next Trans setting but keep the Trans Area as that will make sure the Dissolve and the Rate are kept. You can also keep the Shared Pattern enabled. Now you want to enable the Run Auto attribute.
So what this will do is give you the "hard white flash" where what ever is on air will "cut" to White then it will do a Dissolve (due to the Run Auto) at the rate that you set when you stored the memory. Because you have the PST Bus and Next Trans left to not recall it will transition to the source on Preset and with your next trans settings. If you want it to always go "clean" and not make a mistake with the Next trans buttons then you should store the memory with just BKGD selected and enable the Next Trans Attribute before storing the memory.
Since I was just thinking about this now I don't have a switcher to try on -- however what I will try to experiment with later this week is if it is possible to use Eff Dissolve Recall type and a fast EFF Dis rate to perform a Soft White Flash where it would Dissolve everything to white. I just have never tried to use the combination of the Effects dissolve and the Run Auto in the same recall. So I am not sure if the Run Auto will wait for the Eff Dis to complete or not before running the Auto Trans button.
Les
#Carbonite