I thought that was a brilliant idea,
How does it react to high temperatures - does it leave sticky residue on the board or try to melt?
Possibly. I guess the trick is to put it a safe distance from where you are soldering. I have helping hands made of those flexible tubes and while they are good to hold pcb and components in place, they do not allow for easy precise positioning of two components at the same time. They try to spring back, so if you want to position for example the terminals of a resistor and a capacitor together to make a neat boardless circuit you have to go back and forth many times until you have all aligned. This elasticy is a problem. And can be remedied by using something that allows for continuous plastic deformation.
If you can keep it out of harms way, as should be the case in Youka's problem, you should be fine.
Use the putty to hold the plastic sensor base (that won't get too hot) and the cable. If you are fast enough, the cable won't melt anything, and even if it did, scratch the residues from its sheat.
Not a substitute for every soldering job, just the precision stuff.