i set it to zero and the print never starts. it goes through the process of raising the bed and brings the extruder to temp but then it just sits.

That's because it is waiting for it to cool. This is why I said to set it for ambient.. The firmware that is used in your machine takes temps very literal while another machine we see the temp is low and print. Just look at the idle temp then set it for a few degrees above that. Then it might heat a bit but nothing that will cause an issue and it should start.. But like I said you should print at 60 to 90 on the bed and use hair spray.. You will get much better results.

how do i set my bed temp to be disabled when flashing a cart to run pla?

Just set the bed temp to zero or ambient. Then the heater won't run. Of course you only use no heat if you plan to print on Blue tape. You can still use a bed temp of 60 to 90 with pla if you use glass with glue or hairspray.