In reply to GingerJames:
We had this last year.
The deal is that they usually don't let you extend until a week before your visa is about to run out. You might be able to persuade someone to do it in Ibad.
We were told it was ok to do it in Skardu. Last year, you could not do it in Skardu. We had quite an epic getting it sorted. We had a few choices, drive to Gilgit and miss the first couple of days of exped and risk not getting the visa extension as it was still valid for 25 days, come off the mountain early (no chance) or pay a "local" to sort it out. In the end we had to give our passports to one of the guys at Lela Peak expeditions who took it to Gilgit and then had our passports back for us in Sakrdu when we arrived back out the mountains. Not an ideal solution beint without your passport the whole time you're above Skardu but pretty much the only viable way for us.
The other option is over stay. You can do it, you might get fined. Someone in our camp was being cocky about doing that, but it bit him in the ass when they wouldn't let him fly out of ibad and made him get a transfer to Karachi to pay the fine!
Where did you get your visa from? London hand out 45-90 day visas where as the consulate in Manchester won't give anyone over 30.