I've found that cutting off the neck peg (I use an X-Acto knife instead of pliers, but either way works fine) and replacing it with a neck peg from the AT-TE Tank Gunner (just cut it off and glue it onto the #41 Clone) works perfectly. You could cut the neck peg off of any human character (like if you have an extra Bail or Obi-Wan from the Jedi vs. Sith Battlepack) and glue it onto the #41 body. Then you can hollow out the original head (like Rykrof's) and you have a ball-jointed head.
An easier way would be to use the Ep. II Clone from the Clone Evolutions Set, pop off the Clone head, and hollow out Rykrof's head and pop it back on. Of course, I'd rather sacrifice an AT-TE Tank Gunner and a #41 Clone than one of my precious Evo. Clones

When I made my Obi-Wan in Clone Armor, I cut off the #6 neck-ball-joint and cut out a small hole (since the body is hollow, there is already a hole, you might need to widen it a bit) and then popped in the ROTS Obi-Wan head after soaking the clone body in hot water for a couple of minutes. I had stupidly cut off Obi-Wan's neck peg, so I used a small screw and stuck it into Obi-Wan's head as a substitute peg and that worked fine.
Sorry if my explanations are a bit on the rambling side, I've been hitting the books pretty hard today so my brain is a bit friend
