Massive glass eyes are more robust than mouth-blown eyes. Thus, they can also be set in from the front, i. no cut or hole needs to be cut from the inside to the eye socket, but they can also be set in directly through the eye from the front. How do you do that? By slightly warming your head first. You can use it e.g. put it on the radiator for a while or put it in front of a red light lamp, then the vinyl can be compressed very easily. Pre-fill the eye socket with some foam, then take the eye and gently push it forward through the eye slit. Because the vinyl is soft you can now adjust the eye from the outside until it has the right postion. Often it sits through the foam already so firmly in the eye socket, that you no longer have to stick it. But you can also give a drop of superglue in each corner of the eye, then it is definitely stuck.