I would iron them, and seal them folded in a plastic zippy bag, then they won't move around and get creased, (my daughter is a travel agent, and does lots of long haul trips, she packs all of her clothes this way and it really does work!) and on arrival in your cabin, hang them near the shower, the steam should help, and as you said, after 5 minutes of wear, they will be creased anyway, that's linen trousers, they are cool and comfy, so don't worry about it, they'll be fine!