How can I attach an extended wired keyboard to my Alphasmart Neo?

Like so many appliances and devices now, it has an actual computer inside it. So technically it is physically capable of supporting an external keyboard, but it would require that software to recognize and run the keyboard be built into the device. From the manufacturer's response, it appears they have not included USB keyboard device driver software, which an external keyboard cannot work without.

So in practice, it would require access to the source code for the software that runs the device, and the ability to either port or write the appropriate software to make the keyboard work, then finally being able to add that code to the device's operating system. There are virtually no manufacturers who would ever let someone outside their company do such a thing, so the net result is no, this will never work.