One more option for flying through/over a gliding site is to find their frequency and give them a call. You'll soon find out how they're feeling about transit traffic, and whether you can negotiate passage through. Otherwise I'd stay well clear for my own safety! Having flown gliders a while ago, I remember going solo after about 3 hours roughly (about 6-7 dual aerotows) along with the rest of our group. Not sure I'd had the ability to deal with a rogue powered type.