non-modal file dialog window

I would like to use a file open dialog that does not pause the app. I’ve tried to call ofSystemLoadDialog from a thread, but I’m getting “EXC_BAD_ACCESS” if I do that. Even if that had worked, I would still have to figure out how to make the dialog modal, and set up a callback instead of returning something.
I’m on OSX. Did anyone have better luck trying this?