Hmm. As in. . . it continues updating them so that they cannot despawn? I don't think that would necessarily qualify as 'spawn-jailing'. I don't know exactly how useful that would be. Can you specify some other uses, besides zoos, for said potion?
.... ummm ya bad idea, how about a potion telporting it gives u the ender buff wicth then all u do is look at a block and hit [h] and u teleport
to that block
0
0
0
0
0
0
0
0
1
0
0
0
to that block
0
0
0