Two weeks ago at flameout I remembered that I had forgotten to add whirfloc and Wyeast nutrient. Luckily, I was doing a 45-minute hop stand without additional pre-cooling of the wort, so I just added them at flameout, and as per my hop stand procedure, stirred every few minutes. There was plenty of time for them to incorporate and be pasteurized/sterilized.
I kegged/started the dry-hop last night and the beer tasted great, and had no problem fermenting.