I can’t find a keyboard with them, or a copy/pastable line where they’ve been typed
Maybe use combining diacritical marks?
I’m using 0x326 (Combining Comma Below), but you may need the CGJ in there to render correctly in all contexts
e.g.
Foo!̦ Bar?̦
Edit: Combining grapheme joiner, not zero width joiner
Ah yeah I don’t know how I would do that easily on a phone. Do those in my example above render for you? You should probably be able to just copy/paste them on a phone if they do.