Is there anyway to fix a couch that is sagging?

We have a la-z-boy couch and loveseat, that is a few years old but should still be in good shape. However we have an overweight friend who comes over almost daily and sits in the same spot on the loveseat, causing it to sag tremedously. I would love to purchase a new living room suit, but do not want to spend the money only for it to be ruined by the overweight rutting around of the friend. Is there any way to repair the loveseat from the sagging with out a tremendous waste of expense. It is not the cushions that are sagging they are still in pretty good shape, but the actual loveseat base that is sagging.