What AOPA are talking about is people logging SIC time on aircraft that do not require it or in an operation where the company's policies do not require it. This is not a good idea. There are however many programs where you can pay for training. It IS done, and will continue to be done.
I know one guy who paid $8000 to receive SIC training on a KING AIR. The companies operating certificate specifically allow them to do this. They DO NOT pay him as an employee.
I also know another guy who made arrangements through his foreign flight school to do this with Ameriflight. He paid them a large sum of money and worked as a first officer flying night cargo. The company paid one guy to be there to act as PIC while he got to log the legs which he was actually flying. No logging of SIC took place, some legs he got to sit and watch and other legs he got to actually manipulate the controls and then he logged the time not the captain. This was on a BE-99 which does NOT require two pilots.
I say again, It is done, regardless of what AOPA tell you.