LogFAQs > #975583907

If we're really serious about this, here's how I think it would go:

1) 32 slots in the bracket are reserved. The normal nomination method is guaranteed 224 slots (7/8 of the field).
2) Finish regular nominations.
3) Look at where the bubble is. Host makes a decision where, precisely, to stage the cut-off between 224 and 256. As a result, some number of slots under 32 are actually reserved for auto-include.
4) Contact the users who nominated or supported least successfully, and are above some requisite minimum spent.
5) Those users have a brief window to supply one song to include in the contest.

That's the quick version. There's lots of things I could say about each of these points, but I don't want to make it look overly complicated.

Alternatively we could just give one to everyone, but as noted, that will tie up a huge swath of the field. It would also be dubious to determine that retroactively. Maybe one to everyone with some minimum participation level in the previous contest, and those have to be submitted before nominations. I'm not a fan of this, but it would be an option.