Google announced on Google+ that you can soon login to multiple AdWords account via the top right menu. It basically will let you toggle from one account to the next very quickly.

Google wrote:

Here is a screen shot showing where you click to access the accounts:

To use the multiple account sign in for your AdWords accounts, you can click on your Customer ID or login email within AdWords to open the account selector. Then select to add more accounts using the “Add Account” button.

Forum discussion at Google+.