I got ticked off by a much larger sheep farmer for feeding concentrates in a bucket because come lambing, he reckons that they will still come running to you when you enter the field, leaving their lambs in the dust (or mud as the case may be).
Ours learn very quickly that we no longer bring cake. We stop caking maybe 4-5 days before they're due to start lambing; by the time they get started they're back to ignoring us!

But leaving lambs is only really a problem where there are factors predisposing to poor mothering. First-time mums, lots of twins, very large lambing areas, that sort of thing.
One of my tips is, however you expect to be shepherding during lambing, get your sheep used to you being among them in that way ahead of the time. Then you get less scattering of sheep and lambs when you appear, for instance, on foot with a collie dog. It's usually saving the quick lamb and not getting back to the slower that causes the problem, so the less they're panicked the less they get seperated.