I would not worry too much on the immigration making a problem for you. It is the airline you use to get here that might ask you for one, and you won`t be able to get on the flight without one.
I have never had to show the TM30 in Bangkok. A lease contract has been sufficient so far. However this was 4yrs ago. A workaround could be to book a cheap hostel for a night. I am leaning more heavy on using an agent for extensions these days since the trips to Wattana is time consuming.
Alright, I have never done a TM30 and never had a problem with extensions before. Just wanted to check if something changed in that regard. Thanks for the help!