The addition of a single setting in Engraving Options>Fingering>Substitutions>Alternative, Editorial and Cautionary would make it possible for me to add a single line of alternative fingering without the workaround of text:
Enclosure for alternative fingerings: None
I could then position two fingerings over each other by making use of “Placement of alternative fingerings” set to “Below” and adjust the “Gap between alternative fingerings when arranged vertically” under Advanced Options to allow a line to be drawn between the two sets of fingering.
The same system could be used for chords if all the fingering of the main fingering could be gathered together vertically and the same for the secondary fingering so that a line could separate them.
Although I do not use parenthesized alternative fingering, in my experience, it is generally positioned “Above” the main fingering as with non-parenthesized alternative fingering, not “Below” which is given as the only option. I just checked through the Schnabel and Arrau editions of the Beethoven Sonatas to verify this. And when several such parenthesized fingerings occur in a sequence, a single set of parentheses encloses all of them as a group.