2 Factor Authetication and EAP-GTC

Hello: I have recently been made a part of a project in which we intend to use freeradius. So far, FR seems to be the ideal tool except for one small issue: 2-Factor Authentication. Try as I might, I cannot seem to find any way to set up a multi-factor solution using PEAP. So I suppose my question is this: has anyone had any luck using EAP and challenging the user to enter some sort of OTP? I know that EAP-GTC is meant to do this, but the meager documentation I have on it does not give too much detail. Regards