There's two things to think of regarding taking a dock in the upright position (not necessarily sitting vs. standing). The first, obviously, is taking the dock with your hand. The other is flying without the hand you're docking with. A friend of mine loves to fly upright with one hand on his head. He is able to fly around as if he was using both hands, but always has one hand free. Sometimes he flies upright with no hands Try it... flying like this involves more of your legs, and back than when you fly with both hands. **If you envision yourself docking with your right hand, try flying with your left hand on your head. This way you'll practice the side of your body that is probably less comfortable for you, and when you feel good about it, try flying without your right hand. You'll probably be able to do it without any practice. I swear it works like that! It works like that for pretty much everything in this sport. Practice your weak side, and your strong side will naturally happen. In the end, you will have the ability to fly without depending on either hands.
Taking the dock... If you can fly with one hand, you should be able to fly docked with someone else... It's getting the dock that can be tricky. When you come closer to someone, a lot of people have a tendency to reach out to the person... this will definitely make you move away from them (push you back). What you want to do is move towards them (slowly!!!) with one hand tighter to your body. Stop moving towards them, and reach out a little to take the dock. As soon as you reach out too far, you'll be blown away. I think that docking on someone's foot is probably the easiest sit type of dock.
Oh yeah, one more thing... when the dock starts to make you spin, or you feel like it's not stable, try to let go before it blows apart. This way you'll stay closer to you partner and be able to practice taking the dock, and not playing the good old game of chase your friend around the sky for 45 seconds.
Blue...