Well, what ended up working was:

Lamb/rice kibble, with hot water and:

Dinner broth from leftovers when possible
Sometimes plain fat free yogurt
Sometimes tomato juice
Rarely, cat-kibble tea
Rarely, egg wash
Rarely, pulverized-dog-chew tea

... and about half the time, especially at brekky when there are no dinner leftovers left, GRAVY TRAIN!

I should mention that most of the weight loss occurred while we were away and he was boarded. Jean runs a great kennel, but F was upset at being there so long-- first time on a stay longer than a weekend-- and didn't eat enough. He came home thin, but not so thin a kennel manager would have spotted it. It took another week, once we were home, before I was sure he was truly not going to eat enough--- looking back on it now, I think the dry kibble just reminded him of the kennel food too much, and along with it, the kennel loneliness/ hunger. His entire demeanor was changed post-boarding too-- needing constant reassurance. Now he's back to his old Big Puppy self, except the cat has taught him how to play with string on a fishing pole without wrestling for it or running off with the pole ("stick!!!").

Faulkner once again looks like a normal, healthy, slender yearling. He sleeps better, is easier to get along with, and enjoys the friendly competition over his bowl, with the cat who joined us about a month ago. The kitty is his brekky inspiration, and Hardi remains his evening inspiration. F has nearly stopped raiding the litterbox, too, and empties his bowl most meals-- after a nice long puppy-burpppp. He's very grateful, too-- comes over to thank me spontaneously at odd moments.

Cold weather is rolling down the mountain, so this is solved just in time, and since I leave at the end of October for several weeks, there is also plenty of time for Hardi to pick up the new feeding pattern.

Thanks, everyone, for all the options!

~Susan