Use a single repeating field with at least 3 repetitions and use it in your relationship to get the "OR" based relationship you want.
You can also use a single text field and separate the three values in the field with returns such as this calculation field set to return text:
List ( DiscField1 ; DiscField2 ; DiscField3 )
Either approach will set up the "OR" relationship you want.
A third option is use use a Join table to link your records, but this may not be needed for this situation.