As it turns out, what happens is Whincup takes pole - much like he's done in the rest of his career.
He also lowered his own practice lap record earlier in qualifying to 1min 08.5730sec before handing the car over to Dumbrell.
The biggest hiccup of the day came during his co-driver's stewardship, when Dumbrell appeared to beat the green light and jump the start.
A subsequent inquiry cleared the car, which Lowndes conceded looked "dodgy" but was above board.
"We actually don't know what happened, believe it or not," Whincup said.
"But I think they made the right call."
The lack of championship points didn't reduce the intensity of racing, with both series drivers and co-drivers involved in ferocious fighting for position.
The biggest challenge to car No1's dominance came from the Holden pairing of Shane Van Gisbergen and Jonathon Webb.
Webb jumped five places with an electric drive during the co-drivers' race and Van Gisbergen backed that up by taking it strongly to the series leader during the final race.
Whincup's nearest challenger for the V8 Supercars title, Ford's Mark Winterbottom, completed his best qualifying effort in several races to finish third, with Scott McLaughlin fourth.
The Volvo driver showed strong pace across practice and qualifying.
Holden Racing Team drivers Garth Tander and James Courtney locked out the third row, ensuring they too stay in calculations. New Zealand's Fabian Coulthard will start from 10th.
While the field behind him is fast and determined, Whincup's main worry could be history.
No pole sitter has won at Sandown since Craig Lowndes in 1996, a feat achieved just six times across half a century.
Sandown 500 grid
1 Jamie Whincup (Holden)
2 Shane van Gisbergen (Holden)
3 Mark Winterbottom (Ford)
4 Scott McLaughlin (Volvo)
5 Garth Tander (Holden)
6 James Courtney (Holden)
7 Craig Lowndes (Holden)
8 David Reynolds (Ford)
9 Tim Slade (Holden)
10 Fabian Coulthard (Holden)
- AAP
