Install UE4 once to an external NVMe SSD (USB-C 20Gbps). Set the UnrealEngine folder as portable.
While not a true installer, you can force the launcher to generate local installers: unreal engine 4 download offline installer extra quality
: Paste this folder onto your offline PC. You can run the editor directly without the launcher by navigating to Engine\Binaries\Win64\UnrealEditor.exe (or UE4Editor.exe for older versions). Install UE4 once to an external NVMe SSD (USB-C 20Gbps)