Shane Watson's Sydney Thunder required 187 for victory at Spotless Stadium, but their chase only lasted 5.3 overs before persistent rain ended proceedings on Tuesday night.
The Thunder were 2-34 at the time, with Watson having just hit spinner Mujeeb Ur Rahman out of the park.
But the hosts were still 15 short of the required total under Duckworth-Lewis calculations, improving the Heat to 2-3 this season.
Former New Zealand captain McCullum had scratched together four, four, eight and 14 in his previous BBL innings.
But the 37-year-old released the pressure with four sixes in a 35-ball 56, while Max Bryant (36 off 23) and Chris Lynn (54 off 30) had the Heat on track for 200-plus.
It was a wet end to English pair Jos Buttler and Joe Root's time with the Thunder, who will now depart on international duties.
They will be replaced by New Zealand's Anton Devcich and England allrounder Chris Jordan, who will both be available to play the Adelaide Strikers on January 13.
Brisbane return home to play the Melbourne Renegades on Thursday night at the Gabba. Tickets are available through ticketek.