There isn't (yet) a portable install version but you can achieve something similar by just copying the Agent Ransack installation folder to another folder or drive. The only thing you may want to change is where the user app data is saved.
By default Agent Ransack stores user data in:
If you're running in portable mode you probably want to store that information in a sub folder of the Agent Ransack folder, e.g.
You can change the folder information in Configuration->Folders Settings.