Thats exactly what I did do joe!
When I eventually got hold of them late this afternoon!

(the're an internet based company and dont seem to like taking phone calls)
Their idea is that I cut a large hole in the inner skin of the hatch, big enough for a socket and a small hole in the outer skin so that its only secured on the outer skin.
That gets over the problem of the short studs.
However i still have the problem of the existing fixing holes in the glass!
All I can think of there is to put some tape on the inside and fill the holes from the outside with some kind of mastic.