From what I see from several answers, I may not have explained myself well. Going on vacation and carrying less than the legal minimum is not a problem. I was thinking more of moving to another country, and taking the holdings you normally manage with your Hardware Wallet on your laptop or PC.
I mean, carrying 0.01 BTC on your mobile is not a problem but if we are talking about 0.5 BTC that you manage with the HW....
Although I see that this is pretty hypothetical, according to the answers.
Aside from what other member said. WarpWallet (a variant of BrainWallet which is harder to brute-force) may work, where you remember specific passphrase and email (as salt). Obviously you need to use real WarpWallet and doesn't use common passphrase.
I had also thought of taking the seeds written in a book or notebook on several pages, but with invisible ink, so that no way that it will occur to customs agents to search through a book of 300 pages.
I think most of us only can say "it may work".