Arpeggio into a partial tremolo

I hope I can explain this adequately...

I'm trying to notate (for piano) an introductory chord that starts with an upward arpeggio from A-C-Eb-F in the left hand to A-C-F in the right. From there, I'd like to hold the left hand while the right hand does a tremolo between the A and the C-F. I thought I could do this with a tied chord for the left hand and the right hand does the tremolo but since I want the arpeggio to apply to the entire chord (i.e. from left hand to right hand), I can't separate the following tied chord and the resulting tremolo ends up getting applied to the entire chord rather than just the top three notes.

Hopefully the attachments will illustrate. One shows what I want to do with the tremolo but it doesn't include the left hand chord. As soon as I try to add it, then MuseScore tries to apply the tremolo to the whole chord (as shown in the other attachment).

I could separate the chord but then I lose the arpeggio at the beginning. Any ideas?