LOL,

Here is how I would tackle this. I might tell the person to please put the laptop away as we are in take-off. The person would most likely agree if asked politely.

I wouldn't expect from the passenger to get up off his seat and store the laptop away safely in his luggage because it's too much work and hassle to move things up in an overhead bin while the plane is close to take-off. The person would mostly keep the laptop close to him as it is a valuable and its a LAP-top..... It's perfectly fine this person keeps it on his lap. In fact, I find it natural that he conserve it on his lap.

Life is too short to mind about these tiny nuances.