It may be a bit of an overthink. If the person has any business being inside the box they will check if it is live before licking their fingers and poking around. If the panel is well labelled it should also take the mystery out of figuring it out (it is two circuits, one location).
If a proper item is not available for the purpose I would not "hack" it. If it was a must for you maybe consider something like the CHOMT2020220 and use the two tied inner breakers as your feed for these two circuits, but you can still wire each with a separate neutral instead of a full MWBC but the two are factory tied for common trip. It will likely require some moving things around on the panel (two spaces required instead of one). It also looks like they make a tie bar for two adjacent breakers like you have, which is a similar concept.
Other than that what you are trying (tying two together, but not MWBC) is likely an uncommon application so off the shelf may not be possible.
Not sure for US code (NEC) but it is not uncommon here for multiple circuits in one box, specially for switches. No need for common trip.
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