@nubechecorre
I updated the FilerCX commodity to do something like what you wanted.
Download it
hereThough note that I wasn't able to prevent the workbench from opening it's own windows as well as a Filer, so while I'll keep the code in FilerCX I will not make a big fuzz about it. (And please don't report that it doesn't always detect double clicks, I already know about that.)
It uses the same mouse button as you have configured in the FilerCX tooltypes plus holding down CTRL.
For the techically interested: when I detect a ctrl+double click on an icon I check if it's a folder icon, open a Filer window and use DisposeCxMsg() to get rid of the click event. Unfortunately workbench seems to get the event anyway, regardless of what priority I give the FilerCX commodity.