One way would be for you to generate smart previews for the images you want to work on while you are away from home. The smart previews would be generated on your computer hard drive. You would be able to edit the smart previews with the external hard drive disconnected, and the editing performed on the smart previews would impact the master images when the external hard drive is reconnected. Of course, this would assume that you will disconnect the external hard drive and take your MacBook Pro with you.
Another approach would be to create a collection of the images you want to work on and synchronize that collection. Then, even from another computer, you could log on to Lightroom.adobe.com With your Adobe ID and password and have some limited editing capabilities. Or, if you install the cloud version of Lightroom on your MacBook and have it with you you could edit the images in the collection that you shared.
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