I don't want to tell you to remove them, but I can't think of a frame that you keep the sheaths in there. There are frames where you run full length cabling, there are frames that have cables stops and tubes to guide the inner, and there are ones that run naked inners through the tubes and routed on guides. I don't recall any with removable sheaths that are meant to stay there. I have heard of second hand frames with cables removed that were nearly impossible to feed new cables in. I have no experience with Fondriest though.