Hello all,
Although I don't do aikido, I do study Daito-ryu and I think the body movements are similar. I've found sumo taiso and swinging a very heavy bokuto has done a great deal for my technique. You can find a link to sumo taiso here:
http://www.sumo.or.jp/eng/kyokai/kenko_taiso.html
If this doesn't get what you need I would also recomend power lifting techniques although I haven't done any of that in a long time. I also haven't had any trouble with isolation exercises to strengthen certain problem areas.
Just my 2 cents,