Umm... it's oxymoronic to call it "Aikido atemi". Atemi is just atemi... whether it's karate, jujitsu or whatever... you're striking the body somewhere... with some part of your anatomy. It's independent of whatever (Japanese) style of martial art you do.
Any part of your anatomy can be used to hit - it doesn't have to be limited to hand/foot techniques as in a 'punch" or a "kick". There's also seizing, pressing, rubbing, digging, poking, scraping, gouging etc.
Also, targets aren't necessarily restricted to obvious and gross areas like face, head, and body... pressure points/vital points and various hard/soft target areas are all good. Most people tend to hit a (non-) obvious target when the closest thing being proferred to them is the arm.
FWIW, I think Nishio's atemi (as demonstrated in the Yusuru Budo book and DVD series) is rubbish... and if I were to be more polite - at best, pre-school level atemi waza.
The videos posted by Salim are closer to what I learnt in karate-jutsu and jujitsu, and I think are far more appropriate in terms of setup, execution and follow thru for Aikido 'techniques"... and closer to what I've seen of good hapkido.
I would suggest to the OP, get yourself an anatomy reference and a good set of pressure point charts. Find a list of various hand/fist formations and kicking techniques used in karate (or even CMA in general). And then find yourself a teacher who can teach/show you this stuff - and then work out how you can integrate it into your Aikido "techniques".