Can’t be done currently without a computer. Some HW wallets may do it, but Trezor doesn’t. To do it on a HW wallet you would need a way to copy the private key into the HW wallet without using a computer. This would mean the HW wallet would need a camera, or you would have to type the private key in using the touch screen or something. Another option may be the SD card, but technically that is still using a computer to format and write the private key onto the filesystem.