You probably know the drill. Take the hard lick, slow it down, gradually work it back to speed.
Maybe you've taken a metronome and methodically moved it up one notch at a time.
(A great way to feel virtuous, by the way).
However, it seems that if enough time is spent on the really slow work, the brain "latches on" to the lick and things can take off quickly.
You might get more results by increasing the tempo using more of a "curved ramp."
Something like this...