This is me blocking a XP in Madden NFL 10 on PS3. For this one, I used punt block (lol). I found a way that allows the outside defender to speed around the line and block the kick. Problem with this online is that it completely depends on timing and luck. If I do this against the CPU in practice mode, I can block it 9 out of 10 just because the timing is always the same. So it's not that effective online unfortunately :( lol. You're better off just stick to the traditional way of trying to block FGs.
http://www.easports.com/media/play/video/11895810
http://www.easports.com/media/play/video/11895810