A couple of times (in the same enduro), yrs ago I had a similar (yet different cause) situation. Whenever something slows (or stops) the rotation of the rear tire, the wobble arises and the rear of the bike will attempt to pass the front......if you let it.
In my case, a "lean" running 2 stroke Bultaco when running WFO (around 70 mph), the engine would lean out and lock up solid (no warning......just instantly). Obviously a locked up engine while in gear will likewise lock up the rear wheel and then the fun begins.
The cure in this case is to grab the clutch lever as quickly as possible, which allows the rear wheel to again begin rolling/rotating and the bike will instantly straighten back out. This allows one to coast to a stop and clean out the drawers
So, in a rear tire flat at speed, I'm of the opinion that (likewise to my enduro scenario), pulling in the clutch lever might help the situation even though you indicated getting out of the throttle.