Get a partner and each of you put one hand on each side of the ferrule (i.e. you have your right hand on the top section and your left hand on the bottom section and your partner does the same) then apply increasing force. When I worked at my marina it was the rare rod that would remain stuck although I admit these were always salmon gear rods and not fly rods.
Get a small can of Butane for a lighter-spray the male end of ferrule[top part of but section-this will shrink the blank at that area and rod usually comes apart easily.Spray for about 5 seconds.i carry a can of Butane n my truck incase I ever get stuck ferules.
A bag of frozen corn wrapped around the upper butt section, wrap that in a towel to slow down the melting process. Works like Yamy's suggestion by shrinking the male end. Get some rubber jar openers to grasp the blank, a slight twist and pull, make sure it is in the opposite direction you put the rod together.
I have had some success just leaving it outside over night, the colder the better and trying to separate in the morning. You might try the behind the knees hand on each side and try to pull with the hands and push with your knees. Once apart clean the female ferrule with denatured alcohol.