Aitzaz Ahsan, a 70-year-old Pakistani legal expert, was in Colombo last week for consultations on the matter, a Sunday Times report said.
His visit came after President Mahinda Rajapaksa made an appeal to Pakistan Prime Minister Nawaz Sharif.
Ahsan had defended Sharif when he faced charges of attempting to hijack former military ruler Pervez Musharraf's aircraft in 1999 before he was ousted as premier in a coup.
He was of the view that besides the 12 countries that had voted in favour of Sri Lanka at the UNHRC, only 4 more countries were needed to call such a special session.
He advised that such a session could be used to present Sri Lanka's case to win over more members.
Ahsan's advice has come as the UN braces to announce a panel of investigators and terms of reference for the rights accountability investigation on Sri Lanka as per the last US-moved resolution adopted at the UNHRC session in Geneva in late March.
