B2N2's proposal is the best reply you're going to get for your question.
Considering that this category of aircraft is not certified for Accelerate-Stop performance at all, this proposal comes closest to what is tested and certified for those aircraft that do require it. The 20% may be a bit generous, maybe the equivalent ground distance for, say, 5 seconds at Takeoff Safety Speed might be a bit more appropriate.
Regards,
Old Smokey