The screen you are referring to is 521. SAP has provided for Enhancement option in this screen which you can use to put in your check.
The PBO of 521 has
MODULE DYNPRO_MODIFIZIEREN. Within this module there is a perform
PERFORM dynpro_modifizieren(sapfm07r) USING vw km07r-fausw.
and in this perform they have provided the ENHANCEMENT.
ENHANCEMENT-POINT DYNPRO_MODIFIZIEREN_01 SPOTS ES_FM07MED0_DYNPRO_MODIFIZIERE INCLUDE BOUND .
you can add your code and make SCREEN-INPUT = 0.
Regards