as the guys / gals have said, sitting up close and dropping the clutch is one way to do this. this is a good method and great to start out on but what i have found is most effective is this.
1. begin to just roll the bike a little above idle (i find if i roll at idle i fall off haha) once again your idle may be different due to gearing etc etc.. anyway the main point is to just be crawling along.
2. shift your body forward so your chest is pretty much above your handle bars or above the foam protector to be more precise.
3. tilt your feet downward so your toes are pointing at a 45+ degree angle towards the ground.
4. now one way is to pull the clutch in, give it some gas an drop it, this will rip up fine and generally more than any other method but its also more erratic and can sometimes grab when you dont want it to, throwing the nose of the bike up and if you didnt expect it you will end up in a heap on the floor. the other way is to crawl as you were and just give it hell, pull full power on and this will be a smoother transition of power over dropping the clutch.
to explain the feet position in a little more detail, this is for control and control only, while doing a burnout such as one like this, i dont think your going to need to change gears of use the back brake so you have the ability to change your foot angle. when you have your feet like this is gives you much more control over a flat foot style. this is because if the bike begins to kick out to the left, simply kick back using your left leg and due to the spinning of the wheel and your weight distribution, it will slide back into line, visa versa, if it kicks right, push with your right leg and it will slide back into position.
if you want to drag your burnout ...out... for longer then as binky77 and a few other members said, hold the front brake as this will slow the bikes top speed down allowing you to continue, when your done ease out the brake and evenly distribute your body weight, dont throw your ass back on the seat and sort yourself out too quickly otherwise it may grab and throw you off the back.
hope i haven't missed anything or confused anyone. thanks for reading
Cheers, Tony.