Make use of a cunning plan on half of them (6)
I believe the answer is:
employ
'make use of' is the definition.
('employ' can be a synonym of 'make use of')
'a cunning plan on half of them' is the wordplay.
'a cunning plan' becomes 'ploy' (I've seen this before).
'on' means one lot of letters go next to another.
'half of' indicates taking half.
'them' halved is 'em'.
'ploy' put after 'em' is 'EMPLOY'.
(Other definitions for employ that I've seen before include "Put on the payroll" , "Hire; use" , "Make use of" , "occupation" , "Give paid work to" .)