CI2/3 and CI4 in parallel

Let's say I have a site that is currently a combination of CI2 and pure php.  I will be working on upgrading the CI2 portion to the latest CI3, but as I understand that, it is all in place, such that I don't have to re-write the code to upgrade to CI3.  I've seen the upgrade path and it doesn't seem terribly difficult.
Now, let's say I want to start writing new stuff in CI4 until I can fully rewrite all of the existing code.
the existing CI code base is at www.example.com/path/to/project
assuming I install CI4 at /path/to/project/ci4, is there a way to do URL trickery such that, if I create a HelloWorld controller in CI4, the user could access it by going to:
www.example.com/path/to/project/helloworld and NOT have the 'ci4' portion in the URL path instead of www.example.com/path/to/project/ci4/helloworld ?
Thanks.