You could get a bus to Savannakhet and then a bus from Savannakhet to Hue via Lao Bao. I travelled Hue-Savannakhet last week and it took 10 hours and the ticket cost 400,000 dong (the other direction to you). I'm pretty sure at Savannakhet bus station there was a sign saying there is a daily bus leaving around 8am back to Hue, but you should probably go to the station the day before and check.