I wondered the same thing, or more acurately I wondered if the threshold could be changed using vag-com.
In my A3 the warning light comes on around 50 miles, I'd like it to come on about 25 miles from empty.
If I'm only going to work and back, 50 miles is about a weeks worth of driving!
Whilst I'm on the subject I wonder if the same can be done for the washer bottle warning, I drove all the way from MK to Blackpool and back with the light on (New Years Eve so I was using plenty of water!) and it never ran out - seems a bit excessive to me.