Just bank on setter (6)
I believe the answer is:
merely
'just' is the definition.
('merely' can be a synonym of 'just')
'bank on setter' is the wordplay.
'bank' becomes 'rely' (I've seen this before**).
'on' says to put letters next to each other.
'setter' becomes 'me' (the setter of the clue).
'rely' put after 'me' is 'MERELY'.
(Other definitions for merely that I've seen before include "Just one" , "'Only, and nothing more (6)'" , "Simply - only" .)