Entirely possible. I'm not that familiar with the case as I'm not Australian. Still, this doesn't mean smuggling by proxy never happens and innocents don't get caught up in it.
Heres what usually happens;
- the smuggler is coerced into smuggling the drugs because they have a debt to a crime ring (ie. bikies) and are made to smuggle the drugs as a means of wiping a debt or to keep their family from harm.
(incidentally, one of the Bali 9 was a mates brothers friend, he only did it for this reason, he was 18 at the time from memory)
- someone on the other end of the line working at customs is paid off to turn a blind eye as the drugs come through. It is possible the drug mule goes to the wrong officer or that officer for some reason doesnt appear to be working that day or in that area.
- someone with a small amount of drugs is told everything is setup and is good to go all they need to do is see person X to pass through and it's all already organised. Except they are being used as a decoy, so anonymous tip comes in officials are waiting for person of x description or name and while that person gets all the attention someone else is carrying the main supply comes across less scrutiny as the attention is focussed elsewhere.
Smuggling by proxy may happen but its too unreliable; the person being used as the mule doesnt believe they have anything to hide so they are less inclined to being inconspicious and secondly you still have to tail them after the trip to make sure you can even retrieve the items you smuggled.
Supposing smuggling by proxy was even remotely considered a reasonable method, there is no way in hell Schapelle was a proxy, she had 4kg of weed on her. She's going to notice that extra weight in a bodyboard bag and its obvious the bag would get checked. If that was tour idea of a proxy, you might as well have not even bothered trying to smuggle it as it was always going to end the same way; her in jail and the weed confiscated.