Personally, I just stick the > in front even though HN doesn't apply special formatting to it. Most people are familiar with that convention, either from Markdown or from stuff like emails.
The point of pretty quote formatting is to highlight distinction between your own and borrowed text. But in this case the quote is the main content of the message, so there is no need to format it.
The modern convention for such quotations is called "copypasta": you put your quote in the beginning of your message without additional formatting, and attribute it to the author in the end of your message or in the reply to yourself, or ever in the username of account you created to post the quote (such account would be called "novelty account" because THGTTG is in fact a novel).
Attribution after the quote has additional benefit of giving people the pleasure to recognize the source of the quote themself while they read it.
Personally, I just stick the > in front even though HN doesn't apply special formatting to it. Most people are familiar with that convention, either from Markdown or from stuff like emails.