E3D hotends use a thermistor whose legs are insulated with glass fiber sleeving and clamped down with a screw and washer:
This solution enables the printing of high temperature materials, but it's a bit fragile and after reassembling the hotend a couple of times, the screw will have thoroughly mangled the thermistor's legs and sleeving.
Some knockoff E3D hotends use a (horrible) solution where the thermistor is just loose in its respective hole, and kapton taped to the heater cartridge wires which holds it in place:
This solution seems kind of ad-hoc, and I'm worried about the thermistor coming loose. One advantage is that it can be reassembled arbitrarily often, since just pulling out the heater cartridge also pulls out the thermistor without damaging it. Note that the picture shows PTFE sleeving which restricts the temperature, but you could easily use fibreglass in this situation as well.
Another solution is the stud thermistor:
It screws into the hole that is normally used for the clamping screw. Unfortunately you're limited to around 250C because of the epoxy used in the stud. I've also found that the epoxy fails after a while (regardless of temperature) and the thermistor isn't locked in place any more (it still works, by virtue of being constrained by the heater cartridge wires as in the previous solution but that's not ideal).
Are there any solutions, compatible with genuine E3D hotends, that:
are not limited in temperature by epoxy or PTFE,
can withstand being disassembled and reassembled better than the standard fiberglass sleeving,
is a bit less hokey than a kapton taping the thermistor's wires to the heater cartridge and hoping that holds it in place?
I like the mounting method on my Mk9 extruder: there's a small hole drilled into the heat block, parallel to the heater hole. B3 Innovations sells a thermistor packaged into a small spring. The whole assembly goes in the hole, and a setscrew (gently!) secures it. You could just as well put a bare thermistor into a spring or something similar; it's mainly to protect the thermistor from the setscrew, and from excessive bending.
From your photo, it looks like the same thing would work fine for your hotend.
However you mount it, adding some thermal grease can help conduction from the surroundings.