What does the SkyDrive folder do?
When you install the SkyDrive app for Mac, a copy of your SkyDrive is downloaded to your Mac and put in the SkyDrive folder. This folder is kept in sync with SkyDrive. If you add, change, or delete a file or folder on SkyDrive.com, the file or folder is added, changed, or deleted in your SkyDrive folder and vice versa.
Então, tudo o que você precisa fazer é fazer o download do aplicativo SkyDrive para o OS X e armazenar seu Excel arquivo na pasta SkyDrive. Não poderia ser mais simples.