I think that score is 1.45 million. Now for that to happen everything has to be going great for the person, and they are taking a lot of chances on the Chain Stage with it paying off, and they are they are using the Saglio trick for the second fruit, and getting some really good smashes. They also have every single man to sacrifice for the last hide out stage, and get 100,000 points for the last 3 men instead of the usual 90,000 points that one gets for 3 men.
This is my guesstimate at least. It would be interesting to see what others have to say on this matter.