747FOCAL,
You may have read the FAR's but you didnt understand them
(ii) 115 percent of the horizontal distance along the takeoff path, with all engines operating, from the start of the takeoff to a point equidistant between the point at which VLOF is reached and the point at which the airplane is 35 feet above the takeoff surface, determined by a procedure consistent with Sec. 25.111.
Note the part about
ALL ENGINES OPERATING 
I will admit that in the 747, this is usually the most limiting factor, however that doesnt mean that its an automatic 15% buffer!
Rockhound
It is common for the flight engineer to trim the power levers at any stage, on the ground or airborne, the pilots will remove their hands from the throttles at V1
Trim??? that certainly doesnt include advancing the throttles from 1.3 to 1.6 EPR! IMHO, trimming means that the PF has set the takeoff power, the FE is making sure that ALL four engines are at the same EPR!
Tan.
We operate flights out of a 15,000 ft runway, based on our normal sector length and aircraft type, crews could very easily get to 100ft, abort the takeoff and land again! Do we teach this?
NO. Each situation is different, especially in this world of reduced thrust, so the safest option for 99% of crews is to follow SOP's.
Mutt
Mutt.