What I would do, is build a string, an array would do was well(I just don't use them enough in Crystal, but here is a place I would try them out) and place the details in sorted order. then in your footer, you could skip the entries you don't want and sum up the rest in a formula and report back the number.
Interesting that they don't also want a median, as that counters the extreme values...oh well, give them what they want.
regardless, what you need to do is build a record of all the values in order(one way or another) and then remove the ends....based on what(the size of the set?)
Good luck,
HTH