Aleatoric Temporal Boxed Notation?

I've never heard of doing this, but I a few days ago was working with trying to get a huge phrase have a bracket instead of a slur over it. The results were sort of similar. After looking at your post I attempted the same idea.

1.) Place 2 lines on the phrase. The lines end up superimposing eachother, so move one down to the bottom portion (the bottom one shown is at vertical 13sp)

2) Right click -> Line Properties -> Enable Hooks and increase the space on the top one go mid way (or the whole way and then leave the bottom one alone, your choice. I ended up using something like 8sp for the top and (negative)-8sp for the bottom so that the hooks point up. They're aligned but close so you need to move them to stretch it out.

3) Before stretching, disable the Allow Diagonal so you don't accidentally give an angle if you use the mouse. You're better off using the left and right arrows with tabbing to select the proper vertex to do this. Alter the vertical level if needed. Increase thickness to taste

5) Add a new line and line it up to the edge: increase its thickness to taste. I used 0.8sp
6) Add in the line properties a delimiter ending character like a |. Go into the Style settings for this in the same dialogue and increase its font size. I used 30pt and I had to make the text centered to get it to be on the line rather than after it. You have to fiddle with the settings for this one.

Hope this gives a decent idea. Afterwards I'd definitely create a new palette and drag the results into it so you can use them for later. In doing so it doesn't seem to retain the vertical shift attributes so you'll have to move them around still, but at least the hooks and end characters will be saved. P.S. Tuples would work sort of, but you can't alter the thickness or hook lengths as easily, and you'd have to use extra voices and then have a problem possibly with the timing of the music.
Salut

P.P.S actually as said by another poster a text box may be easier and faster to implement for the main step: add a rehearsal mark, use spaces and line breaks and make the border radius zero. You can also use an extra line with diagonal allowed to make it vertical for the ending line.

Haha, it looks like the original poster has many options available now to play with for this sort of thing.