I would suggest this
http://roundrock.express.milb.com/index.jsp?sid=t102. They have a parking lot large enough to accommodate and I bet they would be willing to make an event out of it to draw in more fans. I would be more than willing to contact them, but I would need to have a general number of participants. The stadium is located in Round Rock, which is just north of Austin. Not sure if anyone still wants to do this but thought I would find out if there is an interest. Respond with a +1 and lets see how many people we can get.