The sentence comes from the first chapter of 《姑妄言》, which is an erotic novel. The full sentence comes as below:
Firstly, it couldn't be the country of Ghana at all. At the time of the book 姑妄言 (1730), most person in Qing Dynasty could hardly have a way to get know about Britain, France or Spain (except being a merchant selling foreign goods or related to one of the merchants), let alone an African colonial. Also at that time the name "Ghana" just don't exist. Westerns call the colonial part of Ghana "the Gold Coast", and there is a native Ashanti Empire in the territory of today's Ghana that is not colonized.
Back to the sentence. “先生” means man with high social status, and “阔佬” means rich man. There is a Chinese blog that specifically analyse the meaning of “效用” and “加纳” in the book. His/Her answer is:
In English, “效用先生” and “加纳大佬” both means vulgar upstarts who buy a position in bureaucracy (to make himself have a higher status), “加纳” means "additional payment" in origin, and in Ming and Qing dynasties it mean the action of buying a position in bureaucracy.
My English isn't very good, so I apologize for the possible grammar or vocabulary mistake in this answer.