Not within Lightroom I think.
The way I would do it is to use the OS to copy the files into a directory on your computer and then unplug the USB drive.
When you open up LR it will want to know where they are (there will be question marks next to all of them and their parent folder). Right click on the top-most folder with a question mark and select "Find Missing Folder". This will bring up an Explorer window which will allow you to point LR at the new location of the files.
You make a new folder and added de photos too, for example: My photos , etc
The problem is I don't want to copy all of the photos to my hard drive, just the ones that I 'added'.
Then just move them within LR. Depending on how many there are this may take time. If they're all in one folder (at some level) you can just drag the folder to a location on the computer that is already within LR. If they're not all in one folder then you'll either have to it folder by folder or bring all of the files up in Grid Mode and then select them all and drag to a new location.