You are not the first to write about this issue in these forums.
You will need to establish your company as the owner of the devices. Call a local apple store and see what you need to provide for them to unlock the device.
Consider DEP, Device Enrollment Program. Use VPP, Volume Purchase Program. Select an MDM, Mobile Device Management. I heard that Apple is now enrolling older devices in dep. You can use Apple Configurator to supervise the device which prevents the use from activating the activation lock.
Business overview"
https://images.apple.com/business/resources/docs/iOS_Deployment_Overview_Busines s.pdf
Education overview:
http://www.apple.com/education/it/dep/
DEP sets your business as the owner of the device and locks down the device with an MDM. Apple's Device Enrollment Guide.
https://www.apple.com/business/docs/DEP_Guide.pdf
MDM -- Mobile Device Management allows an administration to manage your iPad and iPhone devices.
Airwatch, Apple Configurator with Apple Profile Manager, GroundControl, Meraki -- is free or was free, MobileIron or Zenprise
For a comparison see this page:
http://www.enterpriseios.com/wiki/Comparison_MDM_Providers
VPP -- Volume Purchase Program give you a discount when you purchase apps in quantity.
http://www.apple.com/business/vpp/
http://www.apple.com/education/it/vpp/
