Regarding the difficult quote from Theophrastus that "The happy man cannot mount the scaffold to the wheel," I found this confession of a 19th century Parisian: "I demand to expiate it; — I accept the responsibility; — I wish to mount the scaffold." This indicates at least to me that 'mounting the scaffold' to be hanged connotes volition on the part of the condemned. Theophrastus might well be saying that it is impossible to willingly undergo torture, and Epicurus responds by saying that one might well undergo torture willingly to save a friend.
Also relevant are these lines from Shakespeare's Richard II:
“O, who can hold a fire in his hand
By thinking on the frosty Caucasus?
Or cloy the hungry edge of appetite
By bare imagination of a feast?
Or wallow naked in December snow
By thinking on fantastic summer's heat?
O, no! the apprehension of the good
Gives but the greater feeling to the worse:
Fell sorrow's tooth doth never rankle more
Than when he bites, but lanceth not the sore.”