sky28 I wish you all the best with Emirates. A friend of mine had exactly the same problem prior to her initial medical. Despite going on a month long mars bar and pasta binge she still couldn't pack on the pounds and was (by the company standards) underweight ...everything else checked out though, and after giving her some advice on nutrition she got the job.
I don't know how strict Emirates are but I have to say the whole airline height/weight thing needs a pretty radical overhall. I had to survive on slimfast and willpower for weeks before my weigh in, despite having a low body mass index and being a british size 12... I know they don't want porkers clogging up the aisles but there are healthier measures I don't know why they don't use them...