Whole Note Playing Under Other Notes?

In the piece I'm writing, I want one instrument split into two parts: I want a pedal Bb to be played as a whole note at the start of the measure while two quarter notes are played over the whole note during the last two beats of the measure. But the whole note needs to play the entire measure.

Is this possible in MuseScore? I've tried simply using a half note, then making two quarter note chords at the end with the quarter notes I want, but tying in the pedal Bb, but MuseScore reads it as one tie, and ignores the upper changed notes.