You should be able to merge the contacts from the PC with the contacts on the iPad when you sync this information from the info tab of iTunes. You have to import his contacts into an address book on the PC (sorry, I'm not a Windows user) and then you can sync them from that address book into the contacts app on the iPad.
This information was copied from the website linked below.
The first time you sync the Info tab with your iOS device, you'll be asked if you want to merge data, replace data on the service, or replace the data on your computer from the following applications:
- Mac: Address Book, iCal, Microsoft Entourage, or Microsoft Outlook 2011
- PC: Microsoft Outlook, Outlook Express, Windows Addressbook (XP), and Windows Contacts (Vista and Windows 7)