Keep 'South Africa' limited to the Cape, and forceably prevent Bantus from entering.
Dont forget that Whites arrived at the Cape before the Bantu did. There were Khoisan there, of course, it wasnt un populated, but European agriculture would, and did, allow the whites to pretty much swamp the locals.
As whites moved east and inland, they met the expanding Bantu nations, eg the Zulu.
Oh, and of course, you might need to avoid Malays and Indians to do the scut work.