Hello Gaurav,
VOP2 is a way. For example PM is your PDP, then this is the setting in this tcode.
This tick gives you the mandatory pop-up.
So far I could not find a way to meet this requirement through user-exit, simply because this field is not a part of any structure of PM user-exits.
If ABAPer tries, he can find an implicit enhancement point in the program SAPLCOIH where he can put a 2/3 line code to force it.
Regards
KJogeswaraRao