is it possible to save a draft blog post (without having to rename the post)?
Do you mind if someone who knows where the draft posts are hidden can dig them out before they're published? If you're not a journalist who needs to scoop the competition, you may not care about completely hiding drafts, and then there is an easy way to do this:
Add a tag with a name like "draft". Then just tag your draft posts with it, and remove the tag when ready to publish. And modify your blog to not show drafts.
The modification is to the inline directive in your blog. Where it has something like
pages="page(./posts/*) and !*/Discussion", add and !tagged(draft)
pages="page(./posts/*) and !*/Discussion"