I was trying to figure this out just this weekend. My need is to hang in the yard with no trees. I don't have the space for the full setup but I have a couple of thoughts on that.
1. Two equilateral triangles should work just as well....I think.
2. By reducing the height of the poles to just a few inches over the hammock connection point you would reduce the overall footprint of each triangle. Using dejoha's handy calculator you can also play with numbers reducing your seat height to 6 or so inches(just enough to make sure you clear the ground). While not ideal, it provides the comfort of the hammock,being off the ground and reducing the dreaded crash distance should the experiment fail.
This past weekend, I was successful in rigging one end point that was stable enough for my children to hang in (my son is about 70lbs) with the other tied to a fence post in the side yard. It lasted about 10 minutes for my 200# self before the the pole slipped out. I had not secured the base triangle and I knew my stakes were insufficient. I was actually surprised how long it stayed up. I hope to have time to work on it again this weekend and I will try to get some pics posted if successful - my kids would love to get video of me if I am unsuccessful.
I started with 550 paracord I had around the house and a 5 ft 'post' of 2" sched40 PVC.