Using Exec-Program-Wait for MOTP (mobile OTP) with MSCHAPv2

Hello, Does anyone know where I can find some information on how to use the following in freeradius ? I have an external shell script which awaits arguments (username, clear password, and other arguments) and returns an answer for validation. The problem is that I cannot find any lead on how to do this while using MSCHAPv2... And I am not sure how to do this with Exec-Program-Wait. Is this possible without rewriting the module in C ? Is there any way to have the cleartext password sent to the external script ? Thanks a lot Fab