I am not aware of any. You may just need to change the contact name to something that will alert you not to answer.
Jane Smith's contact name = "Don't Answer Jane Smith"
The only other option I can think of would be to give people your Skype Online Number, and have all unblocked calls forward to your iPhone number. Then just manage blocked numbers through Skype. You will have to pay about $60/year to keep/use a Skype Online Number.