Just did a piston soak on the '03 Accord 2.4L (154k mi) using the BMW Fuel Injection Cleaner Concentrate p/n 82140428376 (same as referenced in @The Critic's OP but ordered from BMW of South Atlanta for $32 delivered). Previously I was running Supertech 5w30 conventional HM at a run rate of a quart every 1200 mi.
After comparing other posts from this and other boards, the most convincing evidence that the BMW and X66P substances were the same/similar was the ACDelco X66P SDS
referencing the same components listed on the back of the BMW cleaner: Glycol ethers and Aryl alcohol. That and of course the bottles/fluid look identical and reference the same limitation to not add to the fuel tank.
I largely followed the procedure listed on the drive accord site for the x66p soak. Warmed the engine up to 130F ECT and initially poured 2 oz / cylinder then added an additional ounce ~ 5 hours later. After ~ 3 more hrs I pulled the fuel pump relay/fuse and started cranking with the plugs out. Below photo shows round golden fluid stain on all 4 cylinders, almost reminicent of clean oil (I did this before the oil change). No observed carbon crud. I did find a reference to a GM service procedure not to piston soak for more than 3 hrs since it could result in dissolved deposits reforming.
The aftermath: After sitting overnight (ambient temp in garage was 55F) I drained the oil and replaced with ST 5w20 conv and a new Bosch 3323. Chose to refill with 5w20 since I should know soon if I have reduced the oil consumption. A few more cranks with the plugs out to get any remaining fluid out then reinserted the plugs and fuse. That's where it got interesting. It took a few attempts turn over / start and idle was a bit rough, perhaps I didn't get all the fluid out. All the while it was spewing out more white smoke than the Blue Angles in a diamond formation LOL. After a few minutes of idling up to temp, the smoke subsided and it drove without hesitating for a 15 mi Sunday drive.
I'll update if this works, but in hindsight and considering all the hassle, just dumping a quart of oil once a month isn't that bad!