Yeah, it is a tough question, otherwise I would have suggested someone in the OP.
For ideas, I was just looking at a list of Jewish actors on wikipedia - doesn't have to be a Jewish actor, but should have that semetic look and be able to portray the "New York Jew", as this was a defining part of Bill's personality.
My first thought was Adam Goldberg (Dazed & Confused, Saving Pvt. Ryan, & many more) - he definitely has the intensity to portray Bill, but not the right look. I don't think I could believe him as Bill.
Then I saw Joaqin Phoenix, who did such an amazing job portraying Johnny Cash - definitely has the talent and intensity, and his looks might be close enough to suspend disbelief - but could he pull off the New York attitude?
Not sure about that one.
But, he's the best I can come up with for now.
-Dennis