We have a winner.
So I don’t exactly have the motor core temperature, but the hangar surface temperature close to the motor. Basically I got waterproof thermistor(10K NTC) from amazon and connected one end to ground and other end to temp pin. I tested it will boiling water and melting ice. Seems the beta value is same as the default in vesc.
I mounted it using thermal epoxy and then some jbweld for strength. Like so:
I went for a 4km ride just now. The outside weather is currently 17C. While I was riding the motor temp flattened out at 55C. When I got inside it rose to 68C max and then came down. I guess because it wasn’t getting active cooling anymore. I did a touch test and the can was hot, but I could hold it for a long duration. Also you see noise when I am accelerating, that’s because of induced voltage in the temperature wire when there is a large current flow in a nearby wire. I can probably mitigate the problem by moving wires around.
I don’t understand why the manufacturers can’t put a thermistor in there. No one talks about space constraint, but that it just doesn’t work. 
I’ll actually try to put one inside when I get around to opening it at some point, until then this is a good enough estimate for me.