I vaguely remember reading something somewhere about slopers being more about the wrist than the finger grip per se - and so it was possible to train using weights. Wrist curls, finger rolls etc. - rather than necessarily a more "fingerboard" style exercise. Fundamentally though, I would say if you train open handed you'll naturally pick up a certain amount of training for slopers.
Personally, I never train slopers specifically - but my contact strength seems good enough that if it's not too sweaty I'll just hang them anyway. With the possible exception of la conque; fucking problem.
