How can I modify multiple properties of an Operator in a Panel?

Question

I have an operator that has properties like below

class WM_OT_SceneOpen(bpy.types.Operator):
    bl_idname = "wm.sceneopen"
    bl_label = "Scene Open"

    f_path=StringProperty(default="")
    mybool=BoolProperty(default=True)

    def execute(self,context):
        #some stuff

Now I call this in a panel like this and works

layout.operator("wm.sceneopen").f_path=str(file)

However I also want to be able to pass/modify the mybool property as well during the panel execution but I cant find a way to do that.

This must be possible. But how?

Thanks