The easiest way is to lever the plastic guides out of the flaps that hang down from the wings, then just straighten after wards, drill out captive nut, then you can just about get a nut between the bumper and support bracket and hold there whilst putting a bolt through hole as normal, fiddly but that's how I do it.
For the locking nuts, often a(sharp) drift will do the job, but some may need a old bolt etc welding to them, just curl a bit of thin metal into a tune to protect the alloy, put over nut and weld inside a old bolt etc to it.
tabetha