>>11406184
Well, there's still stuff slaves can do without their hands. The pony stuff mentioned earlier, those hands-free waitress setups, and...uh...that's kind of it, really. I guess there's human furniture stuff, but that's weird.
>mana battery
Sure, that works. Exploit that magical talent she's so proud of.
It's probably the most productive thing you can do with wizard slaves without some convenient hentai magic, really. They're just way too dangerous to leave to their own devices otherwise.

Personally I'd just keep her around for fun, though.
Every night, unless her owner's got something else going on, Elaina's given a choice; sleep, or a chance at freedom. That chance entails being thoroughly bound and finger-cuffed, like so, and left in a room containing her wand in some out-of-reach place. She's also vibed up; settings vary, but regardless it will run all night.
And struggle she does. Her wand's right there, hanging right in front of her! If she can just get it in her hands, she'll be able to free herself and end this nightmare!
But of course it's impossible. Her wand's never left anywhere she can reach in this state. Hanging from the ceiling, up on a shelf, in some unbreakable glass case, so close but so far, often in a spot that'd be simple to reach if only she wasn't restrained like this.
The vibrator is two-fold. First, obviously, is just to torture her, forcing her to cum over and over again or to edge her all night. Second is to keep her from passing out. She chose to struggle, not to sleep, and there's no take-backs.

The best part is watching her agonizing over her choice at the end of every day. After a long, exhausting, miserable day of slavery, she's asked if she wants to try to escape or rest up for tomorrow's torments. Sometimes give her a sneak peak of what's in store for her as a nudge towards the former. Elaina's not stupid, she knows this isn't fair, and she's so tired, but...if she can just outsmart him...there has to be a way...!