How to do a backcombed updo?

i've worn my hair like that....and i too only have two hands !

i bring the sides back into a small ponytail, push it up to make the crown poof up, and clip it in place in the back....then i pull out a row of hair just behind where the headband will go and backcomb the hair behind that (still with the clip in place in the back)...bring that layer of hair back to cover the teased hair and spray it all down like a helmet

What they usually do for those poofy styles is backcomb, as you said, the part that will be hidden - say from behind the fringe to where the ponytail will be, but leaving one layer of the hair behind the fringe not backcombed.  Tease it until its a big poof, spray it, then comb the hair you see (the part you left out right behind the fringe) smooth and lay it on top of the big frizzy poof that was backcombed.  Then clamp it in place with an elastic or barette.  If your hair is long though, be aware that backcombing is damaging, so you may not to want to wear it like this all the time. 

You can try doing the style without backcombing by putting your hair in the half up ponytail, then using your fingers pull the hair on top of your head forward so its poofy looking.  (Try to pull it up evenly, a little at a time.)  You won't get as big a poof that way, but you can still get some height and have it look nice.  Hope this helps.