Spencer from NY did several years ago. I recall hearing not-good things about it.
The better route starts in the same parking lot: take the old carriage road up to the turn at (I forget the elevation), then it's an easy shot to the false summit (as you approach you'll surely grab a herd path) then herd path to the true summit. Come back to the carriage road, and continue on it (now straight and flat). When it starts to descend, watch for a sharp uphill turn to the right (looks almost like a stream bed due to rocks). Follow that path and it will wind its way up and come out on the LT/AT just south of Cooper Lodge. Then tag the summit and come back down Bucklin to your car.
If you want to do the other direction, Killington first, I'm not sure how well-marked the junction is with that path from the carriage road. It used to have a small (foot-high) cairn.
Side note: the Killington summit lodge is under reconstruction, so there's no shelter or water/bathrooms up there right now that I know of.