Negative space equal the length of a string?

I'm trying to create symbols, like the Interrobang (basically the ? and ! combined into one punctuation mark), that are the result of two overlapping symbols. Something like this can be produced with two negative spaces, but it isn't anywhere near perfect.

I've seen this and have tried using \mkern{} and \kern{}, but they aren't working for the width of the text.

Basically, I need a command that will operate like: ? \negspace{?} !. This will essentially type a ?, go back the width of a ?, and type a !. (sort of like the ← key on a typewriter.) Is this possible?

Thanks!