You are free to use my email GPG key, 0xFB596985.  That address just gets forwarded to me. 

Though, strictly speaking, it shouldn't really be necessary.  The best a man-in-the-middle can do to your unsigned transaction is... swap out your contribution with his own...?  I don't think you'd have a problem with that    And on our side, as long as we see 0.5 from someone else we'll sign it, regardless of who is contributing it.