I wonder if the formula used is as simple as
Distance=Squareroot((end_X - start_X)^2+(end_Y - start_Y)^2)
And Distance then is compared to distances you should be able to travel normally or with some effect active (like forcerun).
In that case wouldn't it be possible to allow for a slightly larger distance than normally to compensate for lag?
I know it would allow for a minimal amount of speedhacking, but it would also be more forgiving to all of us, wouldn't it?
(Disclaimer: I am not a programmer so I really don't know what I'm talking about 
)