Fujiwara Keiji (
Gundam 00's Ali Al-Saachez) and
Asumi Kana (
Hidamari Sketch's Yuno) said in the latest
Ani-Com Radio that they've done a recording for "something they can't disclose yet, but will do in June."
For some reason, I believe they're talking about
Bakemonogatari since it is the only Aniplex's show scheduled for July and have yet to announce the voice actors for the show.
My speculation:
Oshino Meme - Fujiwara Keiji
Sengoku Nadeko - Asumi Kana