Cut it. Take 18 inches of 25-40 pound maxima or flouro and nail knot it to fly line. Tie a perfection loop 4-6 inches from the nail knot, trim. UV cure the nail knot. I do this on most of my fly lines, floating or sinking, with a preference for 30 or 35 pounds for most normal applications.
If it's a fresh floating line and the loop isn't compromised, tie the nail knot directly over the loop, don't cut it. It will take on water if you cut it.
Or just tie a perfection loop with the fly line and UV cure it to keep it simple. With a sinking line and short leaders, the knot never really becomes and issue with the guides.