How to make a brewed tea at work?
Why not make it how you like it at home? Here's your best bet (and a very simple suggestion); buy a good thermos. You can get a 24 ounce one for about $30 which will work incredibly well, and last you a lifetime unlike most cooking appliances. When you properly prime a thermos with boiling water, it can keep beverages piping hot for upwards of 12 hours. This lets you avoid trying to come up with a complicated solution at work.

Boil water and put it in the thermos, and seal it. Leave it alone for a few minutes while you brew your tea exactly as you want it. When your tea is ready, dump out the boiling water and pour in the tea, and reseal.

We do this daily for my wife, since she is unable to brew tea at work. She just uses hot water, but it stays hot enough that she can actually drop in a teabag or two midway through the day and brew with no issues. Here is the one we use:
http://www.amazon.com/gp/product/B008FK9NIC