I tried this a while ago, and the app had to convert the movie files before playing it. So it's not really a streaming app. Unless it changed recently?
Theres a file under the map folder I think, Australia.msp, or something like that. Just change that too South Africa, then it shows multimap South Africa loaded. It then also shows South Africa under the available maps.
Once you've installed the app, browse to the folder on your iPhone and replace the current map with the SA one.
\private\var\mobile\applications\(look for the sygic app)\Sygic Australia & New Zealand.app\map\aus\
You just delete the map of the version you download from your iPhone, and then copy the SA one in it's place.
The SA map has all the correct info, POI's, speed restrictions etc.