What are the risk of floating a solid hardwood above grade floor using a clip system?
A product called 'DRIcore' (or similar) would work. DRIcore comes as 2ft x 2ft tongue-and-groove panels made from OSB with a solid plastic bottom. You fit them/install them on top of your substrate (concrete in this case), and then the material they're made of can be nailed into.

http://www.homedepot.com/p/DRIcore-7-8-in-x-2-ft-x-2-ft-DRIcore-Subfloor-Panel-CDGNUS750024024/202268752