I think a lot depends on whether the person is simply a cross dresser (and so I understand they are not necessarily gay or even bi) or undergoing gender reassignment treatment and what stage it has reached, where I do however tend to agree with GiG that someone with the "meat and two veg" should probably be in the male cells. However whether or not the Y Chromosome is a problem seems to be debatable
Does having a Y chromosome make someone a man? | Intersex Society of North America
http://www.isna.org/faq/y_chromosome which unless I have misread it suggests that holding the Y Chromosome in one's make up might not be such an indicator of maleness it was thought to be........
How should one treat someone GRS now without the hanging wedding tackle?