There are not games that are specifically 64-bit otherwise that would exclude a lot of potential players.
There are some games that comes with both 32-bit and 64-bit launchers. Which specific 64-bit games are you taking about?
Simply installing a game on a flash drive may not work. Some games need to have information written to Window's Registry otherwise the game will not run.
Why are you playing games at work? It's a good way to get fired though if that is your goal.