I just did this a few weeks ago with a Saison that wouldn't dry out for anything. I boiled some hops for an hour in 1/2 gallon water, cooled the tea in an ice bath, poured it into the keg, and racked the beer on top. There was probably 1/4 gallon left after the hour boil, by the way.
This worked like a charm. I was really amazed how well the saison turned out. I wasn't expecting much, and I had been very disappointed with the brew before. Like you said, I was ready to dump if this didn't work.
It worked very nicely, and I'm happy to drink and serve the results.