visa overstay, extension

hello - when we applied for our Visa, we were originally going to leav Vietnam on or before Oct 5.  Now, we would like to leave on the 8th.

We have already received our passports back from teh embassy with the visa.  We will be flying into/out of Hanoi.

What can be done to extend the visa?  We will only be in the country for a week, so leaving the passport for a week in hanoi isn't attractive.
 
please advise

Scott