I have never seen a back clamp buttonholer or zigzagger. There might be options to alter the fitting on one of those top clamp buttonholers, but it would take a clever person. It's easier to get a standard low shank for the Featherweight. Back clamp accessories turn up on fleabay now and then, quite regularly. Unfortunately it's not like with the general low shank stuff which is there all the time. Keep an eye out and it will turn up.
This one needs polishing and a bit too expensive for condition,
a ruffler. They are available, if you have time to search and wait it out a bit, better condition and at better prices are likely to turn up.