i don't know if it's possible to be able to nail it down to a set value, as it all depends on the user. The only way to truly get a set value would be to attach a LR atty to one battery, a normal atty to another, and hold the buttons down until the batteries die, but unfortunately the atties would pop first.
you could try putting a greater load on each battery, perhaps a 160 ohm resistor(to represent the 1.6 ohm LR) and a 250 ohm (to represent the standard atty), do the same test, then divide the amount of time by 100, but that's assuming that batteries have linear discharge rates, which they don't, and that the resistors resistance will not change as it heats up, which it will, but at least it will give you some numbers to work with.