Rechecked the league settings just now, and I can't change the waiver system now, even if I wanted to. The settings were visible before we even drafted back in September, and unfortunately Yahoo does not allow changes to the waiver system post-draft. Sorry.
The settings are the same for everyone in the league, at least: you need to make changes to your roster before the slate of games begin on Sunday (one of the reasons why it's helpful to have a balanced and healthy bench) and to your lineup before your players play that week.
Sorry again for the roster/lineup issues, SSSnail, but I don't feel comfortable changing anyone's lineup unless it is agreed upon by league in order to maintain fairness, as in the case of a consistently non-participating league member.
For the immediate future, I recommend maintaining healthy backups for all questionable and doubtful players, as well as for your regular starters on bye that week.