Another option is using the MB for transfer.
You can set the price to 1gil to avoid losing money but it obviously puts the items at risk of being bought by another player and losing it altogether.
If you do it outside peak hours and as long as it's not an extremely popular item it's a decent alternative.

But I agree, at least one small shared inventory would be nice. This game is so incredibly alt-unfriendly and the excuse is always RMT. There are many reasons to play an alt and if you pay extra to do so, you should at least have the option of limited item transfer between alts without having to exclude yourself from regular FCs, pestering friends or risking money/ item loss via MB.