Suppose you have a stroke, and it damages a small section of your brain.
The (cerebral cortex surface) brain is made up of a repeating pattern of cortical columns, which is a structure that connects vertically among it's 6 layers, but not laterally beyond the column boundary. There are connections out the top to the higher order layers in the brain, and connections into the bottom from lower layers, but it's an independent function(*).
As far as anyone can tell, the cerebral cortex is composed of a repeating array of these columns.
Suppose you have a synthetic "plug" that can take the place of a number of cortical columns. You remove the damaged part of the brain and replace it with the synthetic plug.
The plug contains processing units which then learn from the existing connections. The human helps to train the connections by giving feedback: as the plug tries out the connections and actions, the human can tell whether the output is right or wrong, and act accordingly.
For example, if the plug was within the speech centers, the human would have to relearn that part of speech which was damaged, but he would have all the rest of his experiences and knowledge as a basis. His environment and other humans (family, friends) would also help support the learning process.
Eventually, the plug would learn the correct responses to any of the inputs, and it would be a replacement for the damaged part.
Now suppose you have another stroke, and it damages another part of the brain.
Continue the process to its logical conclusion, and you migrate the essence of the person from the biological into the synthetic. This is possible because the information in the brain is not stored in one place, but distributed over many areas. If you lose one area, the information can still be reconstructed from information in other areas.
I can well imagine when the technology gets advanced enough, that rich people might be able to get "stroke plugs" implanted, and over time completely replace the biological portions of their brain.
Is this not a sufficient definition for uploading?
(*) Yes, a glossy, simplistic description.