3d model of the Basin Wrench made by Superior Tool called the "Basin Buddy". Costs about $20 USD and is made of aluminum.
http://www.google.com/patents/US6701807
http://www.amazon.com/Superior-Tool-03825-Basin-Buddy/dp/B007BI7IJA
Not sure if a plastic version works.
basin-buddy.scad | 1.0KB | |
basin-buddy.stl | 104.5KB |