Making an iOS vuforia app for private distribution

I created an app in Unity and want to distribute it privately to a few clients. I made an android version of the app and have successfully been able to create a QR code link from box for easy download and access, but I am struggling to figure out this process for iOS devices. This app would only go out (for free) to maybe 20 max iphones and I would have no way of getting a hold of their phone information ahead of time. The reason I didn't want to go through the app store is because it contains exclusive content that my company wouldn't want getting into the wrong hands. Also, if I could get this process working, I would hope to distribute similar apps privately in the future to other clients. I already have the $99 developer access from apple if that helps in any way. Is there any way I can make this work without going through the app store? Or is the app store the best route for what I wish to accomplish?