I hesitate to chime in here as I barely follow what you are trying to do but if I understand that you want to put a thimble in the center of a line that sounds like a really bad idea. The whole strength of a splice is from the load on the line being nicely on the line and the line stays there because of the friction of the buried end with the outer part. As load is put on the line, the outer part grips the inner part. The more load the tighter the grip. That is why you do things to keep the splice from coming apart when there is no load. Putting a thimble in the center of a line is going to put the loads at some odd angle or offset from the line itself. My guess is that something very bad would happen if you loaded it up.
If I am misunderstanding what you are doing, just ignore what I said
Allen