The JAA are more simple about this! V1 definition:
"V1 - Takeoff decision speed"
The actual calculation however, in terms of Accelerate-Stop distance (JAR 25.109), is that the aircraft may:
"...continue acceleration for 2 seconds after V1 is reached with all engines operating (and) come to a full stop from the point reached at the end of that acceleration assuming that the pilot does not apply any means of retarding the aeroplane until that point is reached
So under JAR a two second gap is permitted on reaching V1 before the pilot does anything, to allow for the decision to be made. The continued acceleration of the aircraft from that point is also allowed for, with both engines operating, for 2 seconds (a long time in aviation).
It seems the FAA won't let you do this. Or should I say if you used the FAA calculations then waited 2 seconds before you did anything you'd end up off the end.
There is a different calcuation for ADSA in an engine failure situation, but it's pretty long and complicated so I won't post it. The above scenario assumes all engines operating throughout.
I used to love the smell of Jet-A in the morning...