Excuse the quality of my drawing but I've come up with this idea and would welcome (constructive) feedback:
Basically, it's a tarp that doesn't need lines going down to the ground (and thus doesn't require pegs) - no lines to trip over and doesn't need soft ground. Imagine a rectangle of material with a tube sewn at each end. Through this tube there is a flexible alloy tent pole that is prevented from straightening by a webbing strap (very common tent design). A cord at each corner keeps it level with two top cords to tension the top.
What do you think?