I don’t say a bracha on Hallel for Yom haAtsmaut or Yom Yerushalayim, simply because Ta’anit 28b delineates when you say Hallel. Likewise, I don’t say a bracha on any other half-Hallel, because I don’t believe in making a bracha on a minhag.
In all honesty, as much of a Zionist as I may be, I’d rather people not say Hallel at all than to make a bracha le vatala on this occasion.