There are some reasonable singletrack trails around Oak Valley, which also has the benefit of being a rather nice vineyard. There are also some good trails in the Lebanon Forest, but nothing too gnarly. Riding is also allowed on Table Mountain, which is spectacular if not that technically challenging.
Might be worth contacting Steve at Daytrippers: http://www.daytrippers.co.za/biking-tours.php as they provide a service to riders wanting to follow and do parts of the Cape Epic route.
The importers of MuleBar in SA might be able to point you in the right direction as well – Rudi at http://www.mulebar.co.za