Along the lines of makeshift training, could you get the same benefit by hip hinging and throwing up a medicine ball high up in the air (or over the head behind you) as explosively as possible? And the other way around you could drive the ball into the ground or thru and behind your legs. Would that 'work' and how would it compare with using kettlebells? I don't have a horse in the race just found myself wondering.
Also I have handle holes in my weight plates. Was thinking of running a band thru one hole and using the other one as a handle to do banded cleans like you would with a kettlebell. Not sure if it would work either (i havent tried).
edit, ok I tried banded plate swings and it works quite well. It's a lot of fun and it gives a nice little conditioning workout, I did like 11 reps in under 20 seconds with a 5kg plate. Overall did about 5-6 sets. Awersome. 10kg plate worked too and I didnt try bigger plates than that. I'm definitely gonna do these regularly now, I needed a quick hip exercise in my training - this is it!!!
I have a question tho - I can definitely see how it helps train hip explosion, but it's almost entirely leaving out the function of the quads. So can this really be sufficient to make one jump higher or would you need to additionally train the legs using a different exercise like front squats or highbar squats? OP said he just did swings and saw increases in his vertical, perhaps he already had adequate leg strength from his past training though. Just a guess.