I'm not on T yet, but I'm definitely one of those stereotypical guys who has sex on the brain throughout the day. I am actually a bit scared of going on T because I'm already horny as hell most days without it, and I only get to see my bf once a week. I know sex once a week is better than nothing, but still...nyargh.
I find 3 things to be helpful: intense exercise, eating healthy, and writing/painting pornography.
The exercise tires me out and gets me that runner's high that is almost like an afterglow AND it makes me feel good about myself and like someday I could conceivably be muscular and sexy. It's hard to get going at first, but I've been working out for a year now and the difference in my strength, endurance, flexibility, appearance, and self-confidence has been huge (65 lbs down, 20 to go!). I bind with sports bras, so I can breathe when I exercise. If it makes me look like a girl I really don't give a crap. I know who I am, and that's what matters. The more weight I lose, the more perplexed glances I get from men and women alike.
Eating healthy, I've found, helps me feel less stressed out all the time. I don't have blood sugar highs and lows, so my mood is more even throughout the day. There's a lot less of the pent-up itchy energy now than when I had a crappy diet.
Writing and painting porn is my other coping mechanism. I enjoy pornography with science fiction/fantasy and BDSM themes, so I get to make stuff that is exactly tailored to what I like. I let myself lie down in bed, have a really intense, trance-state daydream, and then I put it down on paper in one form or another. The intensity of the creative process detaches me from my body, so I am caught up in the trance rather than in frustrated hornyness. It might not work for everyone, but it works for me.
If you need to focus on something else, but you have a raging hard-on, try thinking of really disgusting/unappetizing things. Dirty bathrooms, moldy food, anything that is so-not-sexy. Really flesh out the image in your mind with sight/scent/feel/sound/taste as applicable. You might know this trick already, but if you don't, it's a lifesaver.