My lo is now just over 7 months but he was doing this same thing when he was about 6.5 months.
He got his two bottom teeth at just over 4 months and they didn't seem to bother him at all. Then when his top ones started coming through he started pulling off heaps, doing that pushing off with his hands and 'nipple feeding' like you mentioned, and also biting! And I'd yell 'no biting!' (not in a mean way, just trying to give him a bit of a start) which he thought was great fun and he'd just laugh at me. The advice I got was to end the nursing session when he bit and put him down on the floor (even just for a minute or two). I didnt have the patience for that though so I'd just unlatch and say no and then continue again.
It was my thought that he was doing all of it because of teething (they say the top two teeth give more trouble then the bottom two because they're bigger) and that he would stop when they came through.
Well he stopped the biting and popping on and off when they came through! He still tries to pull off a bit but not as bad as before. I usually just unlatch and wait for a very wide mouth before I put him back on. Sometimes hold behind the head so he doesn't have as much room to pull off and that seems to work and doesn't bother him at all.
Don't worry, it's just another phase (what isn't these days?) I just kept telling myself 'it's just another phase' and it sure was and thank god for that!