There are 3 possibilities:
1. Staffing: McKinsey has a global staffing model and you have a lot of influence on where you are getting staffed. I was part of the German office and only did one engagement in Germany. That is the easiest way to be somewhere else and can be achieved by networking with EM, APs, and Partners.
2. Short-term move: When I left, they were pushing the opportunities to go for a temporary office transfer between 6 months and 1 year, I believe. This should be discussed with your PD and they will be able to point you in the right direction. Often, such opportunities materialize after being staffed abroad.
3. Long-term move: If you want to fully transfer offices, you need a lot of pull from the target office. It's possible but not as easy and based on your question not what you are looking for anyway. :-)