This question has been around for many years, and I recall appealing it as long ago as 2007.
The UK CAA examiners' answer at that time was "Ah but you must assume that the aircraft is taking-off at it's field limited take-off mass, so there is no space available to increase ASDR" When I pointed out that nothing in the question indicated it being a field limited take-off, there was no convincing reply. I believe that most of the schools appealed the same question and got the same response. This was quite common at the time.