I would probably try something between the 2 doses. With him my worry isn't so much rebound, it's that he could be hypoing. Really I don't know, it's just grasping at straws - those seizure things combined with a really high following PS made me wonder if he had some sort of hypo episode that triggered the seizure, or weird symptoms or whatever it is, followed by rebound. If that were the case, it might not be that the dose is excessively high. I would probably try something like 2 or 2.5u.
If he is acting worse though, then I agree that's not the way to go. If you were seeing rebound, the #s should improve on a lower dose. The only times I see rebound-like #s are around the seizure times, so it's hard to say what is cause & what is effect - could be something weird happened in those cycles that caused hypo/rebound and weird symptoms, or maybe just the seizures caused the higher #s.
Pretty much they need insulin to lower the #s. You can lower them with LC canned food, which you are already doing, and exercise can help, but as far as I know in most cases you can't get enough response from that to skip insulin.
Hope things go great for you guys on Lantus, it's so hard to know what is going on with him

but hopefully you can get in more consistent good #s and the weird stuff will go away....