Fitting headlamps to plastic bowls

Hi everyone,
 
I bought some plastic headlight bowls for my Mk2 to replace the rusty dented metal ones my car was fitted with, but have hit a snag. The area circled in red is quite different to the metal bowl, having a 1/4" hole instead of a small metal stand where about a 5mm bolt passes through from the front. This is the only place the headlamp is securely fastened through to the bowl through a hole in the mounting ring (the other two points in the ring being slotted only). I can't fit anything through from the back (i.e. a bolt), as otherwise the back of the bowl doesn't sit flush against the panel. How does the headlight get secured to the bowl in this case?
 
Thanks for your help.
 
 

It seems that the manufacturer of the replacement headlamp bucket (Magnum) leave out the crucial part - a captured nut, as seen in this photo (what a nuisance):
 

 
Martymexico's suggestion is a good one, although as I don't have a rivnut gizmo, I instead carved out a bit of the plastic with a dremel tool, and superglued a nut in place. Hopefully the little buggers stay put.