See here we have the two Herald lights stuck together. Before i did that i crudely cut a hole for the pipe to pass through, and here it is at roughly the right size loosely in place.
Second pic shows my attempt at duplicating Martin.
He used Plasticard to fill the gap at the top of the light section, bent round in one piece.
So, cut this to the right size, spent ages making the pipe hole the right size and then put it in boiling water till soft and wrapped it round.
The thing just went floppy and wouldn't hold its new form. Dunno if its a case of the plastic being thick enough - but that's all the shop has so got to think of something else.