I went ahead tonight and did my conversion work on my Falcon to make it so it can play as a Fire Prism instead.
Started off like this with everything glued in place:
and I then cut off the scatter laser, magnetised it so that I can remove it for the fire prism and also play different weapons.
I then constructed from .5mm plasticard the prism and glued it up as a three sided piece. I ran some green stuff along the edges. It actually fits snugly on the end of the pulse laser without needing a magnet or bluetack to hold it in place.
Pretty happy with it for about 1 hours work all up.
Certainly a good option compared to shelling out for a whole new fire prism!
Will paint it up soon.