@Graham ******
It's not that hard to pull it off yourself. Face it you ain't gonna be the only foreigner there ;)
I'd say from Bangkok fly an early morning Nok Air flight to Udon Thani.
Take the mini van at the airport to the Nong Khai border. Get your Lao visa, get to the thai consulate, turn in your paperwork, go chill at a guest house until the next afternoon, then go get your passport at 1:30 and high-tail it back to Udon Thani in time to catch the 6PM flight back to Bangkok.