No problem.
Even though using your Apple ID to restore is okay ... I get super paranoid about it as well. The reason it asks for your Apple ID when you just format the sub-partition is because you're still leaving the purchase history of the OS on the remaining partition, which I believe is the Restore partition. Just make sure to tell whoever purchases it from you to associate their Apple ID with Yosemite by downloading it themselves from the Mac App Store. They don't even have to fully download it. They can just start the download then cancel it. That way if they have to use the Restore partition, they can now put their own Apple ID in.
This is not the case. There is nothing left behind with your AppleID.
