With the help of an overhead projector and a few corny jokes, the emigration consultant has taken just one hour to deliver a narrative that starts with resentment and ends with the 100, mostly white, people in audience dreaming of a better life somewhere else.
They arrived thinking they wanted to leave the country; now they are queuing to put down a deposit for an individual consultation so they can find out how. "I just want to know what my options are," said a middle-aged man who refused to give his name.
"It's not just about getting a better job. I've got two small kids and there's no saying what kind of future they are going to have in this country, and I want to live to see them grow up. The way violence and crime is going here you never know."
With the country's second democratic election less than a week away, the talk - principally among South Africa's whites - has returned to the subject of emigration.
But while news headlines threaten an exodus, official figures show a 7% drop in the numbers leaving the country in 1998 compared with 1997.
"Some years more people leave than others but there has been no significant increase overall," said Vincent Williams, manager of the southern African migratory project.
But the number that responded to a newspaper ad for Mr Gambarana's "international migration alliance" suggests that the prospect of starting a more stable and prosperous life elsewhere remains popular.
Surrounded by flags of Britain, Canada, the US, Australia and New Zealand, he breaks in his audience gently, talking about the weather, and the Afrikaner communities in Aukland and Vancouver. But peppered between the picture postcard slides and weather charts comes steady confirmation of the disgruntlement many feel at the changes of the past 10 years.
Holding up a book called When Mandela Goes, Mr Gambarana implores his listeners to get a copy: "People, this book is a wake- up call," he says. "The bad news is the paw's really going to hit the fan. The good news is the fan probably won't be working."
Five years after South Africa established a democracy, many people remain eager to leave. Like the audience in Sandton most, but by no means all, are white. A considerable number of Indians and Coloureds from the Cape are also trying to go.
"Our research showed that the number of blacks and whites who would leave the country if they had the opportunity was evenly spread across the races," said Mr Williams of the migratory project. "It's just that more whites have the opportunity."
Even the beneficiaries of black-empowerment policies - the small black professional class which has been created - are thinking of going.
"I don't want to leave but I think there are more chances for me in America or Canada," said Sipho Mandlene, a computer programmer. "I don't want to go forever, but just to see if I could make it over there and then come back with better experience."
A rising number of those seeking to leave are Afrikaners. They once prided themselves on a determination to stay in a country they insist belongs to them as much as it does to the black population. "Sixty-eight per cent of my client base is Afrikaans-speaking," Mr Gambarana said.
According to a recent report, the main reasons given for leaving are growing crime and violence. Other reasons include falling living standards, worsening standards of health and education, government affirmative action policies and better employment opportunities abroad.
Most head for Europe. The next most popular choices are Australia, North America, other African countries, and New Zealand.
But the precise scale of the emigration is unclear, because roughly 20% of South Africans travel on British passports, around 10% have other foreign passports, and many simply slip out of the country without declaring that they are emigrating.
It is not the numbers but the calibre of those departing that worries the government, which is trying to rebuild the economy and society after years of apartheid.
More than half the emigrés are economically active and more than half of those are professional, semi-professional or managerial workers. Their departure not only depletes the pool of skilled labour but pushes up the wages of those who stay, adding to inequalities.
Last year President Mandela delivered a blistering attack on those abandoning the country rather than staying to help build the nation.