Applying from Vietnam just requires an entry stamp to prove you are actually there. I haven't been asked for a Thailand lease. However, if they do ask for one, many people have booked a fully refundable hotel stay on agoda and submitted that. Once they get approved, they cancel the booking.

I was asked for proof of income when I am unemployed. I submitted my service termination letter i received from my old job, wrote a letter specifying I don't currently work. This was hcmc embassy. Maybe try hanoi, or jakarta seems to be quite quick from recent posts