Spit splice before and after, like magic. Sixty seconds, no yarn lost, and no ends to weave in later.
Try it yourself with any non-superwash mostly-wool yarn. Unply 2-3″ of the yarn ends and cut or break half the plies. Lick your palm (or go to a sink and get your hand damp, but really, who has time for that?), overlap the new and old yarns in your palm, and rub your hands together for about a minute. The combination of heat, moisture, and agitation will felt the yarn ends together and you’ll end up with a solidly joined yarn that’s about the same size as the original yarn. The texture is slightly different, but it’s barely noticeable after you knit it up.