There is a Paragon tier feat called "War Wizardry" that gives your attacks against allies a -5 penalty and halves their damage against allies.
There is an Epic tier feat that I can't remember the name of that allows you to ignore a number of squares in your area attacks up to your wisdom modifier.
There is an Epic tier feat that I can't remember the name of that allows you to ignore a number of squares in your area attacks up to your wisdom modifier.