> If this is what it sounds like would it be like making a /path directory and defining it as a union of all the directories containing executables. almost like an efficient and idiomatic way to create a single directory containing symlinks to all of your executables.

That's basically it. Although 'defining' in this case really means 'binding directories into it.'

> How would it handle things like path precedence?

By ordering: first bind the main x86 binary directory into /bin, then bind your custom stuff ahead of it (or after it); as I recall, you could bind to the head or tail.