yeah, that tutorial allows you to sit on the tank using getpos/setpos, but it screws the tank up (it can only move at 5mph, and if the soldiers move it looks crappy.
I had a play with O2 and it is possible, but you will be unable to fire your weapons.
It will use the "Get in cargo xxx" option, and you will sit/stand/lie on the top.
Give me a week and i will put it in the addons beta testing section.