Solution:
- Make dual-boot with some usual operation system, like GNU/Linux or even Windows (less secure).
- Copy the first 1-10 GiB (let’s call it header) of Qubes OS LVM partition and replace if with Fat32/Exfat partition to make it look like an empty storage. Maybe, put a Movie or TV Show there. (Note: Do not use NTFS, it stores its data in the middle or partition and will corrupt LVM).
- The copied header should be additionally encrypted and either hidden using any other ways supporting plausible deniability or even moved online without storing on laptop to be downloaded after crossing the border.
I am skipping some technical details, about partition tables, EFI or grub partition, just follow the idea.