Some good suggestions on non-injury time wasting, like giving a corner instead of a goal kick, or reversing a throw in. Unfortunately, this thread highlights the main concerns with differentiating between truthful injuries and time wasting. I'd also suggest if the keeper goes down, he goes off for 10 mins and they bring on the reserve keeper immediately.
Until the powers that be explore the issue fully, I think there absolutely needs to be some way of ensuring adequate time is added. I would assume the 4th official would be noting this but if he and the ref are too busy, perhaps they need an additional official to advise them.