I remember Kent Armstrong making a back pickup for me in the late '90s, I wanted to get more output but the original was an awkward bespoke shape (5 string jazz type). He moulded the original pickup casing and put the new pickup in. Nice job, visually indistinguishable from the original with more output.
Alas, further down the line I realised that what I really wanted for a fretless bridge pickup, is a humbucker.