Just adding 6 seconds to every hangup is very easy, but do you really want to do that? Imagine an agent clicking hangup, then saying something like "F'ing Ahole!"(although not quite as nice) while the customer is still on the line
Adding an optional feature that would look at the call duration on only outbound calls and add enough delay time to equal 7 seconds(making that number configurable as well) before hanging up the call would be ideal I am guessing. Also, it might be nice to take the call and immediatly send it to a Local/ extension that plays silence so it is no longer in the agent's session. Doing something like this properly, with options in the admin interface, documenting the feature and proper testing, I would quote out at 10 hours to do properly, which would be $2000 for a non-customer, and with our current development workload could be done in about 2 weeks.
Something else to consider is that you would need to make sure your campaign drop time is over 6 seconds, since DROP calls don't always go through the Hangup procedure through VICIDIAL.