On Highend, there is a melscript that will do the work of this for you
It is called RandKey
I cannot post it here, for legal reasons , but go there, and in the melscripts section, do a search for randkey , and you will find it
Here is a blurb from the melscript header:
// randKey.mel v1.1 by Mikael Hakansson.
//
// This script brings up a window, which lets you randomize
// selected keyframes from the graph editor.
//
// It has two modes of randomization. The first mode is the 'offset mode'.
// The selected keyframes will be offset from their current position
// (in time and/or value) within the entered value.
//
// The second mode is the 'box mode'. It will randomize your selected
// keyframes to any time and position within a specified "box".
// For example in the time range 10 to 23, and value range -3 to 8.
// Much like PA's randomize, except that you enter the range values
// numerically, instead of drawing a box in the graph editor.
//
// In both modes there's the possibility to randomize only in time
// or value.
//
// To run the script, just put the script in ~/maya/scripts/
// and type 'randKey' from the command line.
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS
izzylong.com