Forgetting the fact that a piggyback licence is not the best way to go for someone who owns and regularly flies an N reg plane in Europe (the reasons for which have been done to death on other posts), the "No flying, no training" part of Sams post is not correct.
Yes you can be issued the piggyback licence without doing either but you cannot fly with it until you do a flight review. At a minimum this will be 1 hour ground and 1 hour flight with an instructor. However, if you are not familiar with US airspace, charts, regs etc then it could take longer.