Ebay them - just make sure you don't have to wait too long in the post office queue holding them when you go to post them.
Seriously though I would stick in a bucket of salt water and leave for a few days then take to local recycling centre. I had a pack that were slightly swollen (enough to crack the case slightly) because I had stupidly left connected in car and I just put it in a bucket of sand and thought I'd sort it out later. Few days later (4 or 5 days) when I went to sort it out it had swollen out of all shape, almost twisted. Amazed it had not burst. Chucked it in a bucket of salt water (I used loads because I was scared) and it deflated over a couple of days. In future I'll deal with any cells like this straight away because they are not going to get any better.
Rob