I don't have one, so here is just one idea. Maybe an actual owner can chime in. From the photos I saw, I gather the 140 lacks a bow eye for a trailer; that is normally where I see the recommendation for a mooring pendant. Our 23 was on its mooring that way, as is a 19 foot bowrider we have.
I think the strongest attachment point is likely the base of the mast, but if you just tie it there it won't likely hand straight off the buoy. If it were me, I'd rig a line (like 3/8 3-strand nylon, maybe even 1/4 since this is a light-ish boat) with a carabiner or snap hook so it can be looped around the mast base and also ahead of the forestay, at deck level. It would be just long enough to loop around the mast and forestay with just a little slack when snapped around, and would be easy to remove when you sail. Put a small loop into the line at one point, or maybe just use the fitting forming the closed loop, and attach your mooring pendant to that. Seems to me the load would be mostly pulling against the mast base and step, and any sidewys pressure on the stay as it swings would be tolerable.