Oops, I think I've just fixed it myself...

in MPLAB: Project -> Build Options -> Project -> MPLAB C18 tab,

I ticked 'use alternate settings' and appended "-ml" to the text field.

The not so obvious clue was
/* Compile options: -ml (large code model) */
which was written at the top of the demo code screenshot, but not 
included in the pasteable plaintext. After much poking around, I decided 
to try the above, which worked.
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