Cluster events

[s]

For simplicity's sake, lets say I have a cluster with one boolean
control named "OK".  Is there a way I can set it up so that the event
for OK->value changed is executed whenever I write the entire cluster? 
I'm only interested in executed that event when one particular element
of my cluster has changed.  I have tried to wire a cluster wire to a
local variable of the cluster and to a property node with
value(signaling) property selected.  Neither of these signal the event. 
Is there a way?