Lying, as before, on the inside (5)
I believe the answer is:
prone
'lying' is the definition.
(I've seen this before)
'before on the inside' is the wordplay.
'before' becomes 'pre'.
'the inside' is an insertion indicator.
'pre' going around 'on' is 'PRONE'.
'as' acts as a link.
(Other definitions for prone that I've seen before include "Lying face down or likely to do something" , "Recumbent, likely" , "Lying face downwards" , "Given" , "Showing a tendency" .)