"Why do you need "show/explain" anything? If the practice is diligent and concentrated, they will figure it out on their own eventually"
Well, yes and no. I've spent quite a bit of time in the last couple of years training with a big, strong, solidly-built guy who started out doing everything through strength but then began to work hard to use technique instead. So he's aware of the situation but, when training with someone like me who's less than 2/3 his weight, he often needs (and will usually ask me for it these days) feedback on whether he's used pure technique or put in some raw muscle power. This works very well as long as the big strong person is amenable to this sort of constructive criticism.
Paul's suggestion of getting the big person really tired is something I've seen in the gradings in the Jiu Jitsu association I train with. The version of randori used in the gradings is for nage to deal with a sequence (in this case one at a time, but in quick succession) of attackers, who are sent in at a speed determined by the instructor. If the grading examiner sees that nage is using a lot of brute force at the expense of technique, the attackers keep coming until nage is completely exhausted, then another 10 or so attacks are sent when there is no way nage can use strength any more.