If you can find a mutual friend of yourself and the land owner then talk to the friend first about what you want to ask the owner.
My successful experience with this approach did not involve hang gliding but could have been just as sensitive (maybe more sensitive).
A remote B&B in Southern Utah had an invasive non-native tree growing on the property. It was supplying seed for the area which was causing seedlings to spread out on surrounding land. I wanted to ask the owner if I could cut down this tree on their property. How about that for a scary thing to do?
I called a friend of mine who I thought might know the owner and asked him how I should approach this. He said they knew each other very well and I should start my introduction to the property owner by mentioning him (our mutual friend).
I did that and got a warm reception. The property owner said it had been a while since he had seen our friend and asked me how he was doing, so I filled him in with whatever news I had about our friend's recent activities and health. Then I told him that I had a request of him, that our friend thought was a good idea.
Results: The invasive tree is gone along with any seedlings that it had fathered. I'm on friendly visiting relations with the owner and all is well. I think this approach can also work for acquiring hang gliding permissions. Of course it depends on having a mutual friend who agrees with hang gliding activities.
Wishing very good luck to all who try this,