@Syd ******
Okay you need to dial back your paranoia. When you BUY a tourist visa in Vientiane you CAN be asked to show proof of onward travel (within 60 - 90 days) Now how you show this is on you, figure it out.
Also when you stamp IN to the country you can be asked for proof of onward travel as well (although it is rare).
BUT When you go to get your 30 day extension for 1900baht on this 60 day tourist visa you will NOT be asked for onward travel by the immigration office.