- Tag the books you don't want on the laptop with Ωoffline
- Create an Offline virtual library (VL) with search term tags:"=Ωoffline"
- Create an Offline physical library on an external drive.
- Copy the books in the Offline VL to the Offline physical library
- Delete all the format files in the Offline VL
That will leave a record of all the books on the laptop, and provide a separate library for the storage of 'rarely wanted' format files (EPUB, PDF etc)
You could maybe even use calibre://view-book/ links in a custom column to open format files in the Offline library from the laptop library, see
calibre://view-book/
Added: There's also the CalibreSpy plugin, it allows you to open a second library for read only, it would be less work that adding url links (which can break) but not as direct.
BR