a vacuum thread is not the answer

I was just toying around with things, and you know, running vacuum in the
background doesn't work. It slows things down too much.

The worst case senario is when one does this:

update accounts set abalance = abalance + 1 ;

This takes forever to run and doubles the size of the table.

Is there a way that a separate thread managing the freelist can perform a "per
row" vacuum concurrently? Maybe I am stating the problem incorrectly, but we
need to be able to recover rows already in memory for performance.