Is it impossible for this warping to have occurred (if not in the final events of Flood, which I would tend to think) during that 4000 - 5000 years with the non-Flood geologic processes we see at work today (assuming, under the Flood model of course, that an initial, massive amount of sediment was deposited quickly)?
I'm not a geologist so what I say has to be taken with a grain of salt.
Let's look at this:
7 miles is about 35,000 feet in (being generous) 5,000 years. That's 7 feet per year.
The higher crust is somewhat plastic, but since it's not as hot as deep rock it isn't very plastic. What happens to it when you deform it this quickly? It cracks!
That rate of the San Andreas fault is about 45 mm per year (something like 2 inches). You know what happens when it cracks due to the strain, right?
There would therefore be a record of the earthquakes like we have on the pacific coast (but very very frequent and very very much larger). There aren't there ( I am aware of the geologic record of the quakes on the coast - perhaps you can give a reference for the many, many huge quakes around New Orleans) so it didn't happen over the longest possible time frame.
So the warping did NOT (unless you produce evidence) over the long time frame.
Do you now suggest that it happened immediately?
You see, if creationists really thought they had an explanation this sort of very simple calculation would have been done and the evidence looked for. The fact that it hasn't been done shows us that there is no creation "science". There is, instead, a lot of wild-eyed speculation that doesn't stand up to a bit of thinking.