You may consider the use of some Mobile Device Management (MDM) software. Generally, they are subscription-based (per month/annum) per user (device) license, and allow for remote monitoring and management of the device.
Two such products in this area are Fiberlink's MaaS360 or Air Watch, and allow for both app types (public/enterprise) to be distributed from within their main admin portal area. You could upload or point the portal to your .ipa file (no provisioning file needed) and then get it to push your app OTA to any devices registered with the software.
Hope this is of some help as to the alternative app distribution methods out there.