The only option we have right now is to get a retainer. Their is an NPC in each starting city near the guildleve counter where you can get a retainer. They will hold up to 80 items for you. In addition if you put items in your bazaar they do not take up inventory space, therefore you can have an additional 10 slots if you put them up for sale, just put them up for 999k if you don't want them to sell.
I'm sure more methods will show up in the near future, but this should help you for now.