No... although they may be useful for a lot of other things, this (from the User Guide) seems to indicate that they won't work in this case:
"
Event Points
...
post_system: Called
after the final rendered page is sent to the browser, at the end of system execution
after the finalized data is sent to the browser."
<-- there are three of these, this is the only one that is called after the controller is done... by this stage of the game, it's too late.