two legged end for end splice

Someone who has a corodano 15 and says their mainsheet (3/8) needs to be spliced to two 5' legs of smaller diameter (5/32) which attatch to outboard edge of the transom, in effect replacing the traveller. There is a drawing of this system at coronado15.org under "tuning tips" about 3/4 of the way down the scroll bar.
Does anyone know how to do this kind of splice, or heard of it? The only comparable thing I have done is strip the cover off a high tech line and then splice the core equivalent to the bare core creating two legs. Any thoughts appreciated, thanks,
Laurence