There is a bench trail from Fish Lakes that follows the west side of Pipestone valley and rejoins the old horse trail about halfway to Molar Creek, and continues down to the mouth of Molar Creek at the Little Pipestone warden cabin. There are no stream crossings on this section, but finding the start just below Fish Lakes (and not descending to the old Pipestone R. trail) may be tricky if it is still faint and unsigned. I have not hiked up Molar Creek, but others have told me it is rough and mostly in the forest. Not a trip I would recommend.
If you have just one night at Fish Lakes, there are at least two options for returning to the trailhead, besides the usual trail. The most scenic but also the more challenging route is to traverse the ridge SW from North Molar Pass and cross open meadows to South Molar Pass, then hike the trail back to the trailhead. The other, easier route, starts from Mosquito Lake on the N Molar Pass trail and heads south over open meadows until it intersects the S. Molar Pass trail at the headwall, just below the pass. Both options provide the chance to explore S. Molar Pass without having to slog down the Pipestone and up Molar Creek. You can find more info on the site linked from my user profile.
However, if by chance you are 'forced' to spend a second night at Fish Lakes, e.g. on a weekday during bad weather when several bookings are likely cancelled, then I would recommend a day trip to Pipestone Summit via the highline trail (the extra hour to Clearwater Pass is an option, or 1.5 hours to Upper Devon Lake). On the third, exit day, you could still add a S. Molar excursion if desired.