Portable Dropbox/Google Drive

Use DropboxPortableAHK.

The beta version (v1.6.8.14) works with the more recent versions of Dropbox.

A little off topic, but if you are storing "sensitive" information you should consider encrypting your data locally before floating it up to the cloud. TrueCrypt is a popular cross platform solution...

Or, you can just use a "cloud drive" service that is configurable (ie: you can control which files and folders sync, not just a dumb "drive" folder in your profile) and has client-side encryption built in. I've had great success with SpiderOak - 2GB for free + more for referrals.