I used two chains attached to the top of the power rack and attached a single rowing handle (shown at: http://www.newyorkbarbells.com/im-0011.html ) on the end of each chain. The handles are about 10" off of the ground. This is the closest alternative to gymnast rings I have found yet. I have always wanted to add these into my routine as I have heard they are great for hypertrophy/coordination. The only problem is that the cheapest set of rings I've ever found were over 300 dollars.
I will be trying these out tomorrow after DE Bench and will be very pleased if I experience some soreness (which I have not had in my delts or triceps for a LONG time).