EXS 24 Logic Sampler Users Group

I'm trying to reproduce an effect I had on my old and trusty EMU E4 
which worked a treat for getting realistic drum and string staccato 
samples.
Basically you had a number of different versions for the same note 
(staccato var 1, staccato var 2), each assigned to a different 
group. Then, in the modulation page you could setup a random lfo or 
random trigger that would randomly choose between the groups you 
assigned everytime you hit the same note. Since it did this on a per 
note basis, the same chord played  number of times would always 
sound different and hence, more realistic.

I've tried to reproduce this in the EXSmk2, but to no avail.
What I've tried so far:
-set up a number of samples assigned to different groups
-use a random lfo to modulate the destination: sample select

although it does seem to switch randomly, it does so while the 
sample is playing, giving weird and unusable effects.
I need to find a way to only have it randomly choose a group on the 
start of a note (or more exactly, the triggering of a note) and not 
*while* it is playing.
Anyone got any ideas of how to achieve this?

Cheers,

Joris