IF you don't want to change the keyboard, which is the final solution to the problem, you need to do some jugaad.
My favourite jugaad is to insert a small piece of paper between the two conducting layers of the keyboard. To get there you need to pop out the key (not easy if you are using island type keyboard), and then use a needle to increase the gap between the two layers, and insert a small peice of paper. This prevents the conducting pads from coming in contact - which is what causes the signal to be passed continuously.
Mind you, if one key fails today, it is just a precursor for the rest to follow. so eventually other keys will malfunction, similarly.