The inauguration of a man named Greg

Sergeant Major Greg Lowery stands in for Donald Trump. Photo / AP

For a brief moment yesterday, a 53-year-old man named Greg stood on the balcony of the US Capitol, being sworn in as president of the United States of America.

Greg's only qualification? He's the same height as Donald Trump (aka the real President-elect).

Greg - Sergeant Major Greg Lowery, that is, a performer in the US Army Band - joined a cast of dozens who recreated the presidential inauguration as a dress rehearsal for the real thing.

"To be announced as the president, it was a surreal moment. But it was pretty cool," he said afterward.

The dress rehearsal - a quadrennial spectacle that features stand-ins playing everyone from Supreme Court justices and Cabinet members, to diplomats and former vice presidents, to Trump's and vice president-elect Mike Pence's children - allows the staffers running the inauguration to work out kinks in the ceremony before Saturday's main event.

While the fill-ins stood in position, staff adjusted microphones to the proper height, tested out equipment and marked in tape on the floor exactly where each person should stand on so no one gets blocked in the photos. This way, it was not the first lady-elect but a volunteer who had to hear, "Melania, take a step to your left, please" until the tape was in just the right place.

The rehearsal ran in real time.

At 9.30 am local time, "Ladies and gentlemen, welcome to the 58th presidential inauguration" boomed out from speakers facing thousands of empty folding chairs and the expanse of the Mall beyond.

Lowery, who as Trump's stand-in walked out last, got into the part, beaming and offering a regal wave to a nonexistent audience.