I've got a little trick with these connections I think. I have a pointed tip on my iron. while the connection is in a vise I put the tip through the hole on the side then feed the solder thought the hole where the wire will be. Then with the solering iron tip still in the hole i put the already tinned wire in, then pull the iron out. With deans too while on the subject its better to have them fitted with there opposing plug to avoid warping.