If you're an emacs user, prefix the line with the desired number of spaces then type M-q, copy back into your browser. That's my solution to formatting block quotes at least. Your long line prexixed with 3 spaces in emacs:

    So a paragraph that would run off the page and break mobile
    devices in normal circumstances should be broken in several
    places by a hard 'return' plus more spaces.

And your split-by-hand block quote:

    Is really just a collection of sentence fragments that all
    fit the same formatting. There might be a better way, but I
    don't know it!

You could include an angle bracket.

> 32. Although I believe foregoing exchange demonstrates DPR's intention to solicit a murder-for-hire, I have spoken with Canadian law enforcement authorities, who have no record of there being any Canadian resident with the name DPR passed to redandwhite as the target of the solicited murder-for-hire. Nor do they have any record of a homicide occurring in White Rock, British Columbia on or about March 31, 2013"

Or an angle bracket, with an opening and closing asterisk.

> 32. Although I believe foregoing exchange demonstrates DPR's intention to solicit a murder-for-hire, I have spoken with Canadian law enforcement authorities, who have no record of there being any Canadian resident with the name DPR passed to redandwhite as the target of the solicited murder-for-hire. Nor do they have any record of a homicide occurring in White Rock, British Columbia on or about March 31, 2013"

This means you don't need to include any line breaks.

Just use fmt(1) or par(1).