I would have thought Earle would be covered as an injury dispensation.
If I have understood correctly, when a player is injured, you still pay their salary (unless the contract says you don't, which seems unlikely, unless you've signed someone on pay as you play due to previous track record) and their salary counts towards the cap. If they are then injured, you can bring someone in of a similar standard and while you still have to pay them (obviously), their salary does not count towards the cap, subject to a maximum of £400,000 to cover all injury replacements.
So if we got someone in to cover Earle, we'd still be paying him and it would count to the cap, and then paying any replacement (I don't think there is one) but the replacement's salary wouldn't count towards the cap.
If we register Earle as a player on loan then we still pay him but his salary doesn't count towards the cap so long as he plays fewer then 4 games for us in the season (and each game he plays his salary counts on a pro rated basis). That's my understanding anyway. What I'm not sure about is whether you can register a player on loan so their salary doesn't count towards the cap, and then still get injury cover for them. I would guess not, as then you get two players and neither salary counts.
So, again assuming my understanding is correct, if you know that a player will be injured for most the season (or can't play for some other reason, including to comply with the cap, like Lambert maybe) you can register them as on loan and their salary doesn't count, or if they get injured during the season then you get a replacement in and their salary doesn't count.
In the case of someone like Lambert I suppose it is a slight loophole in that, if he is out on loan, his salary doesn't count towards the cap as long as he doesn't play enough games (and from memory did he just play in A league, cup and then fewer than 4 proper games?) but he can still train, so he's helping make up numbers in training, passing on experience to younger players, etc