What I ended up doing was overriding the open function entirely:
elFinder.prototype.commands.open = function () {
// custom code
};
(Just do this in a script
block after loading the elFinder code.)
I can't say if it's ideal, and it will take some tweaking if there are major upgrades to elFinder, but it's definitely doing the job. (Going from this, I also started overriding some of the other functions which use the URL, such as the anchor tag in the info pop-up.)