Sadly, my project wasn't quite as magical as that sounds. A better title probably would be, "running wires without drilling MORE holes."
I'm currently living in a rented house. As with most (all?) rented houses, I can't run around drilling holes wherever I feel like it. I also can't fix anything I see that's broken, which is very strange to me. It's practically a reflex for me to fix broken things I encounter. Unfortunately, this house isn't wired with ethernet cables, and we want wired ethernet in two places. We tried to mess around with ethernet over coax cable a little (something called MoCA) since we had an extra cable modem, but it didn't work out. Here's what I wound up doing.
The house is already wired with coax cables, and it's possible to get to where those wires are run. Fortunately for me, every place the coax cable went through the wall or floor, the hole was oversized. It wasn't enough to push an ethernet cable through, let alone it's plug.
The first trick is to disassemble the ethernet cable instead of the house. I already have an ethernet cable that's pretty hacky, a while back I spliced two really long cables together. I'm sure I've introduced a huge amount of noise into signals going through that cable, but so far I haven't noticed any significant loss of bandwidth or increase in latency.
To get the cable through the hole the coax cable was already in, first I cut one end of my ethernet cable and stripped the insulation (outer plastic shell) off. How much insulation is up to you. Ideally, you should only strip off enough to get the wire through the wall and solder the end you cut off back on immediately after the wires come through the wall. The other side of the floor I was going through was the ceiling of our garage, and I didn't feel like doing mid air soldering that high above my head. I stripped off enough of the wire's insulation to reach the plug I was aiming for, since I was lazy.
The second trick is to use the coax cable (or whatever cable is already there) to help run your new unbundled ethernet cable. I discovered there was enough slack in the coax cable that I could use it to run wires. To test, I made a small sharpie mark on the wire and pulled it through from the other side until I saw the mark. Once I was sure it had enough slack, I taped the unbundled ethernet cables to the coax cable with scotch tape. What kind of tape probably doesn't matter, as long as it holds. I imagine something like electrical tape or duct tape might get stuck inside the hole and make running the wires more difficult. Once the ethernet wires were securely attached to the coax cable in a pattern that fit through the hole, I just pulled the coax cable through. When doing this, I suggest you have one person guiding the ethernet wires in from one side while someone pulls from the other side. I almost lost a couple wires inside the floor when some tape ripped off.
One thing to be very careful about when stripping wires. There's a good chance you'll nick the insulation of the inside wires, I did in a few places. It's probably a good idea to inspect the entire length of the wire as you run it and once you're done, and you should cover any nicks with electrical tape, hot glue, or ideally, heat shrink tube.
While running the wire around other parts of your house, there are other tricks you can use while avoiding drilling holes. Zip ties are great, if you're running along other wires like I was you can just zip tie your new wires to the others. You can also open old zip ties using anything pointy enough (lift the tab that prevents you from pulling it open), and if you're feeling daring you take take out existing mounting screws, rearrange things, and put them back. Personally, I avoided that since running screws in and out would have damaged the holes.
Anyway, this project has a happy and successful ending. A couple hours after I started, I switched my desktop over from a cheap wireless USB adapter to wired internet. It's been running great since than, no hiccups.