All the time.
The trick is to be patient with yourself as you speed up the passage; you MUST use a metronome. Find a tempo that you can reliably play the passage at. Play it at that speed several (at least four) times. Increase the tempo by AT MOST four beats per minute. Play it several (at least four) times. Ideally play it multiple times in a row perfectly before moving the tempo up again. You need to stick to a tempo and play the pattern many times at that tempo before increasing. Once you reach a tempo that you start to feel frantic, don't continue faster yet. You have some other shedding to do.
At the point you start to "break up" you want to back the tempo off several steps in your process. This part can be done without a metronome depending on how you do it. You need to break the passage up into various groups. If the passage is essentially rapid 16th notes (or whatever, as long as it's the same value throughout) you can do this rather easily. Start by making the rhythm double-dotted:
____ __ ____ __ ____
Then try it reversed:
__ ____ __ ____ __
Then try groups of three:
_ _ _ .... _ _ _ ... _ _ _
It's hard to diagram in text, but maybe you know what I mean. The idea is to break the long pattern into very short groups, then mix the groups up and expand them longer and longer until you are playing the whole passage.
I hope that wasn't too wordy...
M.M.A., D.M.A. University of Illinois at Urbana/Champaign: B.Mus. Lawrence University
Bassoon professor at University of Wisconsin Eau-Claire
Maker of the Little-Jake electric bassoon pickup and Weasel bassoon reeds