
Well if you have a valid souble-entry or a multi entry visa it is possible to do a visa border run to Laos, but you can't avoid the Lao visa.
If you have some kind of a legal multi entry visa you do a border run where you
1. Exit Thailand....making sure you get that exit stamp in your passport.
2. Walk into Laos...entering Laos and getting that visa.
3. Turn around, exiting Laos and getting an exit stamp form Laos.
4. Then re-enter Thailand, geting an entry stamp on the next valid entry of your double entry or multi entry visa.
Nothing at all illegal about that, although the immigration at the border may not have seen that procedure before. Their supervisor however SHOULD be aware that what your doing is legal...hopefully he or she will.
No need to spend any more time in Laos than what you require to need to get that visa in your passport
But that's all dependent of you having the double entry or multi entry visa with at least one valid entry left.
If you use Laos however....they're going to insist on that Laos visa anyhow.
If you're willing to go through the Malaysian border then you will find that most Europeans...and certainly the U.K. and U.S.A. nationals can get a visa on arrival to Malaysia,,,,no cost I believe...and only takes a small space for the stamp in your passport....not a full half-page.
But that's another subject.