Take the lense out, wrap the foil tightly round the perspex block and carefully cut a hole where the LED will poke through.
The problem with the foil cake case is that:
1) there’s no glass, so the LED is open to the elements
2) it’s metal and might short across the LED if you’re not careful (maybe a bit of tape to insulate it?)
3) it’s fragile because of point 1
The light created looks great in the garage (and is an improvement IMO on the basic use of it as a torch) but on the trail when bombing along you feel as though the light pool is black in the centre as there’s no penetration to the beam at all.
The mod to the lens works well, don’t be afraid to be rough with the ‘machining’ as the majority of the beam focus is done using the outer egde of the lens.
Ben