I dont know your current charger and what you want to achieve; But:
If it's just to ensure, the temperature is right, I find that a temp gun helps a lot. Once the charger is adjusted properly (charge rate, cut off), there usually aint a need for temp cut off. Only if there's a great change in ambient temperature. But in this case the temp gun will do fine anyway.
And the temp gun can be used for several other purposes
If you want to make your current charger NiMh compatible, you might as well consider a new charger: The LRP Pulsar Sport is very good and can be found for 100$. 44$ more than the temp sensor...
The real down side about temp cut off is if you forget to mount the temp sensor - that can ruin a pack very, very fast