Winsorized mean

I want Excel to calculate the Winsorized mean of any given numbers. There isn't a function designed to do that (or I just can't find it). Does anyone knows the easiest way to do this?

For those how aren't acquainted with the Winsorized mean: http://en.wikipedia.org/wiki/Winsorized_mean

It would be super if I could choose between entering a percentage or a specific number of values to be adapted.

Anyone up to the challenge?

Thanks in advance,
Aliaz, teacher