The way I solve this problem (and perhaps many other users, too) is simple: I don’t use virtual environments. So I pip install everything that I need for such scripts in my main (not system) python and then everything… just works. (I agree that knowing the dependencies is useful even in my case, but using something like pip-run seems heavyweight.)
This is a case where venvs are a classic non-solution to a non-problem, except in the edge case of conflicting dependencies (see also my rant here). But those are not really solved by this proposal, since it doesn’t specify version numbers.