Focus on getting to Athens with your miles. ATH-JTR is a cheap flight you can do with Olympic or Aegean Air. Aegean is part of *A, so if you're doing a *A award, you can include ATH-JTR in your award booking, but note that Aegean awards are only bookable (with UA or AC miles, at least) within 6 months of flight date. Search now for ATH-JTR in July and you'll see availability every day through 7/1-7/12. 7/13 will be bookable tomorrow, for example. So you may not want to wait until 6 months out to book your award (as Adam said, grab transatlatic flights as soon as you can). In that case, just pay for ATH-JTR.