Can I get a visa exemption on arrival and apply for a Non-Immigrant B visa in Vientiane if my clearance certificate is delayed?

Bit of a long question: I was sent back to South Africa for my Non-Immigrant B visa (teacher), and am supposed to fly back to Thailand on the 20th of April. However, the clowns at the South African police are delaying issuing my clearance certificate, and I won't be able to get my visa before my flight out. I have in the interim been issued with a new passport (no previous visa with notes saying "send back to SA to change visa). Would anyone have any idea if I would be able to fly in and get a visa exemption on arrival and then apply for a Non-B in Vientiane?