I also don't have a heat sink on my Jato, and I'm pushing probably, at least 1.5 - 2 times the weight due to the 3mm thick solid aluminum chassis
Just put a hole like the nitros have inline for the motor or ESC... Whichever is getting the hottest... Maybe a 3/4 - 1" across if you make a round hole, or if you go the square route, about that length on each side...
Come summer time, I'm probably going to be sticking a heat sink on my motor just to be safe.