disable 2 sma ports on the rt-n66u

[heuvep]

Hello,

i am running 3.0.0.4.376.45_0 on a asus rt-n66u.
It has 3 antenna's but i want to disable 2 of then and connect a external antenna. How can 1 disable 2 of the 3 antenna's (sma) so i can connect a external antenna with a 8W amplifers.

Is this possible in the sofware to disable 2 sma ports?

greeting Pierre