What's the most efficient way to notate double trills?

I'm writing a duet for violin and viola that involves a lot of double trills (i.e. double stops where both notes are trilled simultaneously), and it seems to be unnecessarily difficult to notate them and achieve correct playback. DoubleTrill.mscx demonstrates how I'm doing it. In particular, I'm attaching the second trill symbol to a note in a silent, invisible, second voice, silencing double stops that are not trilling correctly and writing out these trills as tremolos in hidden staves, to get correct playback. I'm not using tremolos in the visible staves, because trills are easier to read.

In this thread: https://musescore.org/en/node/137676, Marc said that you can click trill lines and then click the accidental in the palette to add it. If he meant the Note Input palette, then this doesn't work in MuseScore-3.6.2.548021370-x86_64.AppImage on Ubuntu 20.04. Instead, I have to select the trill line, press "Z" to open the Master Palette, select "Accidentals" and select the accidental there. The trill ornament is even worse -- I have to select the note, press ctrl-T, press F2 and select the accidental from Common Symbols, which only seems to provide tiny double flat and double sharp symbols. Are the full-sized symbols hidden somewhere in Musical Symbols? There's no "Accidentals" section there. I know I can change the font size, but that would just make the process even longer.

There are a number of issues that make the above process even more tedious than it already sounds:
1. Selecting the second-voice notes that need to be hidden involves either: a) pressing F6, unticking "All" in the Selection Filter, ticking "Voice 2" then shift-clicking or drag-selecting the notes; or b) ctrl-clicking the head, stem and tail of each note individually.
2. Poor initial placement of trill lines for notes that are above the stave -- see InitialTrillLinePlacement.png. I take it this is a bug.
3. Inability to copy/paste trill lines. After shrinking the line and perhaps adding an accidental, it would save time if I could copy the result and paste it onto another note. This doesn't work if there's no accidental, and if there is an accidental, the paste attempt causes MuseScore to crash (I can copy/paste a trill ornament with an accidental though).
4. Spacing changes can cause a trill line that I've shrunk to grow and run through the accidental -- see TrillLineAccidental.png. I haven't worked out the exact circumstances under which the lines grow, but the need to keep manually adjusting them is irritating. Trill ornaments don't suffer from this problem, but vertical spacing changes sometimes cause the ornament and accidental to shift vertically by different amounts, meaning that I have to reposition the accidental (again, I'm not sure of the exact circumstances).

Note: the bugs that I mentioned in issues 2 and 3 occur in MuseScoreNightly-202201230419-3.x-2513676-x86_64.AppImage too. The accidentals in the Note Input palette do not affect trill lines in this version either.

So is there a more efficient way to do this? It seems to me that the ideal solution would be:
a) if trill ornaments/lines were associated with each note in a chord, rather than with the whole chord, so that you could directly add them to as many/few chord notes as you like;
b) if you could use the Note Input palette to add accidentals to trill ornaments and lines, so that you don't have to keep opening some other palette (obviously, playback should match these accidentals); and
c) if trill lines started after the accidental (this is how they are notated in Behind Bars, e.g. on page 135).

PS: I'm aware of worldwideweary's alternative suggestion for correct playback at the top of the thread above. Since I'm already using hidden second voices in the visible staves, this may be less inefficient than the hidden-stave solution. But it's still unnecessarily inefficient.