Perhaps the more advanced aikidokas pratice them, i don't know! Chokes are a dangerous attack, it can stop the oxygen from reaching the brain and even making someone faint
I don't know, really... But if you are so willing to pratice chokes, ask your sensei ^^ Perhaps he/she will teach you some techniques!
Look at this video I found :
http://www.youtube.com/watch?v=WfnWWiISIKc <---- Atemi from a front choke.
Peace