OK, after rereading what the kind member 40to332 told me, I only just noticed it's my english knowledge (or lack thereof) that held me back here.
Add-a-circuit I had no idea what it was, and now I found out, and yes, that will definitely solve the problem of tapping into the fuse
I ordered two now (one for backup in case I want to add whatever else), so I guess that will solve it.
In the meantime, I took some time today to continue preparation for installation, I pulled the sensor wires through to the engine bay. What I found easiest is to guide the wires from the driver's footwell, in front of the shifter, then to the passenger footwell, and then via the cabin filter slot. There is a soft foam "wall" above the cabin filter and I guided the wires through that. They go out in the engine bay right below the plastic cowl that is located under the windshield. It's not the best solution, but it'll work. I fixed the wires so there's no rubbing on the chassis and left them near the battery for now.