Hi Eric,

(1) First of all activate Developer mode from top of the right side corner on clicking on the Administrator(or user you logged in the system)

(2) After then create the Lead record with the customer you want to make default.

(3) After saving the record on the left side on the top the form view there is one selection box Debug View# click on that & you will see Set Default window. There you can select the default values for Lead object.

Thanks,
www.acespritech.com