Fitting rear bumpers that have defuser/spats

Hi guys

this is a "how would you do it" question.

I have a new rear bumper. I have tried lining it up for fitting. So far the ways I have tried is:-

1) Lining up the top holes (by the lights and centre boot). This means the sides clear the wheels arches, however the top corners dont meet the rear quater panal.

2) Moving bumper underneath car and then lifting up. Sides clear arches fine and 1/4 panal would line up but numberplate light backing gets in the way and cant line the top up.

I guess the best way would be to get 2 people to hold it either side and slide it on straight lining up all the holes in one go. However I am unsure if the spats/sides would clear the arches

This is what I mean, the part by the wheel arch curves around like a sideskirt fitting, however it also has a bottom plate so has no flex either.

You'll have to get two people to go on each back corner, go straight in and flex the bumper to clear the spat area of the rear quarters until the bumper can tuck behind the arch. This is what I had to do with my trial. As long as its not painted, but flexing a bumper in the manor which is painted may be a real bad idea...

ahhh it is painted... well will give it a go if it cracks it cracks.

What sort of skirt/difusser is that attached to the rear? Looks sweet, never seen that before

Its the Border Racing kit.

Will look like this when its done