I started doing stand-ups by getting the wheel in the air sat whilst sat down, then once the bike was near balance point, I'd move myself into the stand-up postion. I could keep the front up for a while but nothing compared to sit downs.
Just couldn't get used to the extra weight being put forward.
So I then started experimenting with a 'staggered' stand-up position, (left foot on pillion peg, right foot on the riders peg). I now ride along, straighten my right leg, then place my left foot on the pillion peg and clutch the bike up. This position allows the front to come up with little effort as your weight is now towards the back end and over the rear wheel. It also allows you to adjust your weight easier and with good throttle control. If you try it though, be very careful with your throttle as the bike is very easy to flip. I never do any of these wheelies in first gear. Most are in second but I do tend to bring the bike up in 3rd and 4th
Using this method, I've found I can stay on the balance point for good lengths. Done a fair few over 1km. Just need to find a road long enough to try a mile!