Salutations ,
Unfortunately I cannot provide you with a zipped version of the launcher itself.
However, you can download zipped versions of the editor directly from github which you will then be able to build from source:
https://docs.unrealengine.com/latest/INT/GettingStarted/DownloadingUnrealEngine/DownloadZip/
You will then be able to run directly from a removable hard drive so that it can be portable as you request.
I highly recommend against this unless the portable hard drive has very good read speeds.
It also may not work cleanly (requiring additional work) because of all the system dependencies, I cannot confirm or deny this last bit though.