listen listen listen, and I spell it from top to bottom. then bottom to top, and I try to get as many notes as I can hear. Then, I look at what Im playing and see if the theory would suggest something close to what Im playing. Basically trial and error. And Im not the one to spend a ton of time trying to get the exact voicing anyway.
Another thing I try to do is play the run with the right hand and and see if that puts me in proximity of what I was hearing, and try to go from there. Most of the pros play left hand chords with the right hand adding to it and doing runs, so I always check what voicing would fall in line with that, unless I can tell for sure that they are not playing it that way.
It also pays to know who is playing and/or their style of playing. Like fmason3 was talking about on one of his videos that Mike Bereal and Jason White are all west coast musicians and they all use rootless left hand chords. Thats a major piece to the puzzle, because if you know its them it just eliminates tons of possibilities, and you can focus on the crazy stuff that might work.