I read somewhere about 'darning' by putting the darning wool in approx the right place and letting it stick. Sounds fab but I've no ide how it would work.
Meanwhile best option probably to turn the most worn one into patches for the others
If you are really cunning you take off the sleeves and swap them round, just before they expire, thus moving the outside of the elbow to the inside.
I tried this twice but was confounded by the machine stitching on the garment - worked fine first time with hand knitted/hand sewn together woolly jumper.