Hmm, let's see...
1) Change CCCD6 to 0x1, which tells us we don't care if you've beaten the game on both modes.
2) Sift through the routine at CDD38, which hardcodes displaying the third promotion to the three trainee classes.
3) String of comparisons at CCE72, hardcoded again, tell us what class to display for the third choice on the promotion menu.
4) String of comparisons at CDB80, another hardcoded place, tell us what class to actually promote the unit into.
...maybe I should write a patch that unhardcodes all these parts.