If it's not too much of a deal to you, just let the friend request stick until it's cancelled. That way they can't spam them at you. I was Spirit-bonding in Urth's Gift one night, and got one, so I declined and deleted it, and they just spammed it at me. After I started leaving it, it would take 10-15 minutes before it was cancelled out and another 5 for it to come back.

^_^