FAA rules -
ATC can not waive 91.117, the 250 below 10 rule. However 91.117 (d) says if the minimum safe speed of an aircraft exceeds the limits stated in 91.117 the aircraft can be operated at that minimum safe speed. No requirement to request high speed. ATC knows a "heavy" departing on an eight or twelve hour flight will be exceeding 250 when it cleans up. The one exception ( that I know of) is the O'Hare departure in Chicago which requires 250 until ATC approves a higher speed. Clearance Delivery normally asks heavys to "confirm you are able to meet the speed and altitude restrictions of the O'Hare departure." I reply that we'll make the altitudes but are unable the speed, that we'll be climbing at 275 and request they pass that information to Departure.