The answer is no. You would have no way of getting past security in Terminal E. There is also no practical reason for doing this even if it was possible. The walk or bus ride from Terminal E to either B or C is rather long, and you would have no reliable way to know when you flight is leaving. All domestic flights (except for Southwest, which is in a separate part of Terminal E) depart from terminals A,B,C.

According to Lufthansa, the new lounge in Boston will open in August/September of 2011, but no specific date has been given. The old lounge was not well liked, so I imagine the new lounge will be a big improvement.