I'm not sure he can. I'm not sure any of the current spinners can. Lyon might have the best chance at it (or Hauritz), but if you're going to play him with 3 loose cannons eg. Johnson, Siddle, Bollinger (say Harris gets injured again..), then I don't think Lyon can do a holding job by himself against good players. So IMHO, one of the fast bowlers need to be able to bowl a holding role.
You are presuming here that Harris gets injured and if that is the case then sure pick Copeland to give the attack some stability.
However if its a case going forward where Harris is going to be fit regularly, then Bollinger has to play. Bollinger also isn't a loose cannon quick, Johnson and Siddle more so fit that description, since lets not forget Bollinger before the dumbass selectors started treated him like a fool before the 2010/11 Ashes (along with his injury) - he was bowling leading AUS test attack like a true spear-head mixing high pace with accurate lines and lengths between West Indies 2009 - India 2010.
He showed further evidence in the ODI series in SRI that none of that ability is gone and he really should be taking the new-ball with Harris in tests, of that it really shouldn't be much debate AFAIC.
With regards to Lyon, i think although he will have tough days ahead, i think he showed enough evidence in his first test that long term he can fall into the traditional off-spinners role of bowling discipline lines and lengths at one end for long spells while the quicks attack/rotate at the other.
Plus also a firing Bollinger/Harris/Johnson three-man pace attack should be taking wickets and be fairly accurate too i.e how Anderson/Broad/Tremlett or Bresnan were doing for ENG recently. So its not a situation where every test we are going to need a spinner of Copeland like quick to hold down and end because we are worried about the aforementioned quicks leaking runs like a bursts pipe.
I'd keep going with Copeland to see how long as he's effective, because he's a better donkey bowler than any of our spinners. And the more Tests he gets the better we'll see about those concerns: How sustainable is a 125kph bowler? How will he go on flat pitches? If Australia can't take 20 wickets and need a quicker bowler, OK get rid of him, but until then I love what he brings.
If i were to guess i certainly think his pace makes him sustainable in tests especially if he can move the ball - look a Praveen Kumar recently and i recall seeing Copeland bowl on live internet stream on some green wickets in shield cricket last season and he really seamed that ball around alot - which tells me he might me more dangerous in overcast conditions. In S Africa he could a interesting if AUS encounter a greentop and decide to play an all pace attack for eg.
On flat pitches as we saw in the 1st test he may be forced to being the donkey seamer. But if the other two quicks + Watson can reverse swing the ball and the spinner can get the ball the turn on when those flat pitches begins to wear, he would have still done a job.
So really i think overall he has much use in the AUS test team, just that i dont think he should be starting ahead of Bollinger at all.
We and most AUS fans were in unity in selecting Copeland for the opening test since we all felt the need for an insurance policy bowler who can tie down and end, given the worries that was around about how eratic the quick's (Johnson) could be and how a green Lyon might be target by the SRI batters.
However as aforementioned, the performances of Harris, Lyon, Johnson and Bollinger (in the ODIs) tells me that the need for Copeland's skills on a regular basis is not that important for the test side as we may have thought coming into this test series after the Ashes debacle.