Just yell at people to be in the office for 2 days per week for no reason? Meh. Why?
Organize a week to have all local and international employees together for a week once or twice a year, schedule big organizational meetings and important discussions in that week, sponsor dinner and lunch together, have a team event or three? Just accept that concrete and hard productivity will crash for that week, and consider it a social event? That's actually nice and valuable.