Is there ANY way?

[Ultima Shadow]

...to get the status effect "Shell" on Rydia without the aid of another party member?

Like... is there any item in the game, or any augment that makes it possible?

[Roogle]

The Elven Bow will cast Shell when used as an item; however, I am not sure whether or not you can use equipment as items without having the item equipped.

[a random ninja]

i'm pretty sure you can't. but i'm sure if you go to gamefaqs.com and look the game up, you can find an item list that can tell you if there's any other items that can do it.