For those of you who don't use a mouse broadcaster and have to do things on each individual computer with your mouse (like me), I found a cool little script to accept a battleground port message:

The following will accept the "enter battleground message?":
/script AcceptBattlefieldPort(1, 1)

The following will leave the battleground:
/script AcceptBattlefieldPort(1, 0)

I have bound this to two different keys and it works great.

-Oathbreaker