The duo joined the party on Monday after management gave the Springbok players the day off after their nailbiting 21-20 victory over New Zealand in Rustenburg on Saturday.
Coach Jake White has already hinted he may experiment at full-back for the match, having used centre Jaque Fourie in the position against the All Blacks. Russell may be the ideal starter at number 15 against the Wallabies.
Pietersen is uncapped but has had two exceptional seasons for the Sharks in the Super 14 and Currie Cup.
He has been called up in place of winger Bryan Habana, who will be examined this week after what team officials called a "mild concussion".
The Boks broke their five-game losing streak with victory on Saturday but will be looking to end the Tri Nations on a high note against a team that has already beaten them twice in this year's tournament.