It's done!
It turns out my parts car had the tube in question, and still in good shape. The night before last I replaced the knock sensor and the hose, plus the alternator. I used the squeezing-my-hand-under-the-manifold method since I had to do get used to doing that anyways in order to pull the broken stub of hose off. It became painful after a few times, but it wasn't too hard to remove or install the sensor that way, even though I had to use my left hand despite being right handed.
In the process, I broke the brittle 1/8" L-shaped vacuum hose under the front of the manifold.
Eventually I scrounged some clear tubing of barely larger diameter, and painstakingly collared it over the 2 broken ends. (I did a little McGuyvering too, John.)
BTW I found out that squeezing the little white wings on the sensor's electrical connector do not disconnect it
(or do anything). That's done by a tiny push-down/in lever on the grey connector that plugs into it. Additionally, I routed the wire in a slightly more accessible path.
The next day my hand was all swollen, a little less so today, but still achy.
