I carry a couple of bungy cords with me. I have removed the steel hooks and replaced them with alloy carabiners (the really cheap ones) though that detail is not strictly relevant here - but it does make them lighter and easier to use, I find.
I also carry three lengths of braided nylon cord approx 1.5m long, with a loop tied in each end, which I use to guy one of my walking poles. I then bungy the antenna pole to that.
Now, to your question - if I can't get pegs in the ground, and there is no fence post or trig point, I use one (or two) of the guy lines to extend the bungy. That way, I can get it around a rocky outcrop, or some feature in the top tier of the summit shelter etc.
Sometimes I do that anyway, if it is the quickest option.
In this photo I used two bungies and one of the braid guys to reach an anchor point at the back of the smooth boulder on Tonelagee: