If you want to add initial commentary on the link,
  write a blog post about it and submit that instead.

This will immediately get flagged as blogspam though.

Yes, there was an instance recently where somebody did just that and the link to the article changed to the original link that was being commented on.

That brings up the question: what's considered blogspam and what's considered good commentary? Is that automated, or is there a judgement made by the moderators?

Will it though? I can think of plenty of blog posts that were commentary on links (albeit fairly extensive and/or insightful), that didn't get flagged as blogspam. OTOH, if all you do is editorialize on a link, with little to no insight, shouldn't it be flagged as blogspam? Perhaps one of the biggest reasons I don't blog very much is that I don't feel like I'm contributing anything of value by merely linking somewhere and going "isn't this cool?" I believe blog posts should have more substance.

I am still waiting for https://www.mycustomhackernewsheadline.com where you can add minimal context to a link and submit that to HN.

I was thinking of using http://gist.io for this, but a service that let's you minimally blog, and submit to HN with a single button click would be ideal :)

You can also just use scoop.it which is designed to do just that.

What's the dividing line between commentary and starting a discussion with a primary reference? I've come to really disagree with the strict title rule. IMO, HN should be more of a community for sharing ideas than a simple link aggregator. Someone submits a link because they found something interesting about it and wanted to share. They should be granted some agency to frame the discussion.

The rule just seems overly bureaucratic and inflexible. Often the link is appropriately titled and the content speaks for itself, but not always. An original title arguably has just as much potential to negatively impact discussion as a badly editorialized title. For a Wikipedia article - why was it submitted? For a link titled simply "Jolla," how is that even remotely useful? What the hell is that and why should I click it? For a normal article, maybe there was a particular angle or interesting small bit of it to highlight. Enforcing the creation of your own "wrapper" blog post also smells of unnecessary bureaucratic overhead. Why is it better to trade a "privileged position at the top of the page" for a privileged position at the URL of the link itself, that is now misdirecting from the actual piece (aka blogspam)?

I can see the downside, for example a popular article where multiple people attempt to put their own spin on it, fragmenting and confusing the discussion. But this happens already, how many different threads introducing Amazon Prime Air were there yesterday? Eventually the community settles on the preferred one and the rest die out. It's a trade-off, and would take some subjective tweaking and moderating (which is already necessary anyway), but I think discussions could be substantially improved by allowing the submitter the chance to "start things off on the right foot," when appropriate.