1. Create a post with a suitable title in blogger.
2. Change the post options to make it a scheduled post by publishing it.
3. Go to the scheduled posts lists, open this post and save it as a draft.
4. In flock (and possibly other off-line editors) create a post with an identical title
5. When you publish it select the "Replace Existing post option"
6. Your scheduled, draft post will appear in this list.
7. Publish to this existing post - this will not change the scheduled publication date
8. You can also use this as a means of saving your drafts online at blogger.