Is a man's portrayal of a female role - given the necessity of the character and the impossibility of acting with a woman for fear of khalwa (private seclusion with a member of the opposite sex) and its prohibitions - considered the forbidden imitation of women?

It is not permissible for a man to assume the role of a woman or imitate her, because the Prophet, peace and blessings be upon him, cursed men who imitate women, and those who imitate them are not among them. Caution must be exercised regarding a woman acting [in a play or film] due to the potential for unlawful seclusion (khalwa) and forbidden gazes.