I have another solution to this circumstance if you can avoid an option of cloning different Apple IDs. The main objective is to have an app on your developer's iPad.
Make Sure Your Device is Backed Up.
First, your iPhone or iPad should be backed up either to iCloud or to iTunes on your computer. If it's not, plug it in and launch iTunes. When you see your device in the sidebar, right-click on it and choose "Transfer Purchases from..." (if you have the sidebar disabled, click File > Devices > Transfer Purchases from....) to get those apps off of your device and onto your computer.
Copy the App to a Safe Place for Future Installs.
Once your purchases are transferred, visit the Apps tab in iTunes, find the app you want to back up, and right-click it. Select "Show in Explorer" (Windows) or "Show in Finder" (OS X) to reveal its file location. Then just copy the IPA file to Dropbox or any other location for safekeeping. When you're ready to install it again, sideload it. Just drag a copy back from that safe location back into the apps list in iTunes when your new device is connected. You'll need to log in to your Apple account (here you can change your password or you can log in by yourself), but once you do, iTunes will install the app on the next sync.
I hope this solution also makes sense for you as you are looking to have an old application install on other iOS devices.