I saw that it is possible to install a theme from a zip file but cannot update it.

wp theme install http://s3.amazonaws.com/bucketname/my-theme.zip?AWSAccessKeyId=123&Expires=456&Signature=abcdef

I would like to ask if it would be possible to add this feature, the themes I need to update I have them as zip file and they are not available in repository, also being active or parent themes I cannot delete to install them again.