I understand your predicament- however finding the dog a new home will only worsen his condition not improve it -and I promise you there is not a person out there to willingly take that on.
Is the dog crated while you are gone? If not- buy a crate and train him to it- eventually ( yes even at 6years) he will come to see it as his safe place. Our pup howled every time he was crated- he had severe separation anxiety- and now 6 months later he willingly goes to his crate and at night will sleep in it on his own with the door open.
Walks,walks and more walks- exercise is the best brain medicine there is for both humans and animals
Hire a dog walker to come in and walk the dog once a day while you are gone OR take home to doggy day care
I really urge you to reconsider- there is no way you can hold the next owner to your strict stipulations- there will ever be a better owner than you. You really can't hand off a problem dog and expect it's going to have a better life. Trust me on that one- my 3 were lucky - they ended up with me- but they are in a minority. 4951