Hi, for what I know is better if you keep him on insulin, even a very very small dose but keeping it consistent as long as possible to give him a better chance of a strong remission, if his numbers rise so that he still needs a shoot he may not be quite ready to be on remission even if he is very close to it.
I would suggest that you post your question on the Lantus Forum so that the real experts see it, they will be able to help you better, and if you can add a link to your spreadsheet if you have one so that they can more easily see what's going on it would be better because they will need more information on what dose are you currently givin him and what his numbers are to give you a better advice