Remind your friend he or she has given you full unfettered access to their account. All they need to do is deregister the device using the method Pirate gives and then you can register it. If it is locked with a PiN, they need to give you that code or you will have to enter random numbers until the device offers to reset itself.
Their refusal to deregister it makes me wonder if it was really theirs to begin with and perhaps it is "hot" since it takes 30 seconds to deregister a sdevice.
NOTE: I do NOT speak for or represent Amazon in any fashion. This is a customer to customer forum.
Disclaimer: I have examined any sites I provide links for and have determined them to be safe but I make no promises about safety, content, ads served or anything that might make you clutch your pearls in horror. Use discretion clicking on links provided by total strangers such as myself.