They have not. And, if memory serves me, no team outside the Top 10 in the first CFP poll has ever made it. OSU can win out and get a NY6 bowl but in no scenario can enough happen to get them in the top 4.
You are correct in your first sentence. No two-loss team has ever made the CFP.
However, two teams have made the CFP outside of the top 10, eight (Oklahoma) and nine (Ohio State) years ago, respectively.
Oklahoma was ranked 15th in 2015.
Of more import, Ohio State was ranked 16th in 2014.
Arizona and Georgia lost to allow Ohio State to slide up to 14th.
Ohio State upset Michigan State at East Lansing to pass Michigan State. Auburn, Kansas State, and Notre Dame also lost. Ohio State passed Nebraska, who was off but whose loss had been to Michigan State. Ohio State also passed an overrated and cheating Ole Miss, who spent the weekend beating up on Presbyterian. That allowed Ohio State to jump from 14th to 8th.
Oregon State beat #6 Arizona State 35-27, and Ohio State leapfrogged Baylor, who was utilizing their second bye, because the 10-team Big 12 did not have a Championship Game at the time. That allowed Ohio State to jump from 8th to 6th.
Ole Miss upset Mississippi State to allow Ohio State to jump from 6th to 5th.
Ohio State crushed Wisconsin 59-0 to finish as one of the four 12+ win teams and earn a berth in the CFP.
Ohio State was shipped the the Mercedes-Benz Superdome to play Alabama in a
de facto road game and then played Oregon in Arlington in the National Championship Game.
Oregon State needs to beat Colorado and pass at least two of the teams ranked 1-15 to lose to remain on pace to pull a 2014 Ohio State.
In 2015, Oklahoma jumped up to #12 and passed Michigan State, which had lost and fallen back to #13. Both Michigan State and Oklahoma made the CFP in 2015.