specifying module dependency versions with the present playground

[Dan Kortschak]

I am wanting to demonstrate some difference in behaviours with
different versions of a dependency using the present playground.
However, the go.mod file in the directory holding the code is ignored.
Running the commands that golang.org/x/tools/playground (the backend
I'm using) respects the go.mod file.

What do I need to do to make the present tool use the specified
dependency version?

thanks
Dan