Run the code in a web app, and have the various PCs ask the server to run this code on their behalf.
Do you really want to make sure the user's have .NET 4.5? (answer: no)
You could probably get a Rails app on Heroku in less overall time.
By the way, if you are using Gmail, you can put an OAUTH token on the user's machine instead of your password, which you can revoke. It's still a password of sorts, but at least it's not your password.