Prefetch Settings

Is it possible to change the prefetch setting so that WinXP only prefetches if you have accessed a file a certain number of times?

My PC is prefetching installer executables that I only use once! :confused: !
If Windows has to load all these before it starts, surely it is slowing it down. Right?
I know that you can delete the prefetch files manually but it would make more sense to set a value of 5 accesses before prefetching.
That way you are prefetching the most frequently used (and thus most likely to be used) programs.