You don't need a return ticket, you need an onward ticket out of the country. Just buy a cheap bus ticket which takes you from Nong Khai to Vientiane within the 60 days. It's the airlines who check your travel when checking in. They don't understand about the 30-day extension deal.
Yep. As Lisa has said, best option is get the 60-day tourist visa from your embassy. You're stamped in for 60 days, and you can extend in-country for a further 30 days