I looked at doing this about 12 months ago and was told that although Ryanair was taking non-JAR licensed pilots, they had stopped because they had too many FO's but not enough Capt's.
They also told me that a type wasn't enough, you had to have time in the 73, preferably the NG if you wanted to be considered for the DEC.
If you wanted to go the FO route, they would validate your FAA certs and give you 12 months to get the JAR license. No upgrade until you had that little green JAR license.
Oh, and Ryanair do not consider the CL65 of any variant a JAR 25 aircraft!