Use yours truly, backing stratagem (6)
I believe the answer is:
employ
'use' is the definition.
('employ' can be a synonym of 'use')
'yours truly backing stratagem' is the wordplay.
'yours truly' becomes 'me'.
'backing' is a reversal indicator.
'stratagem' becomes 'ploy' ('ploy' can be a synonym of 'stratagem').
'me' back-to-front is 'em'.
'em'+'ploy'='EMPLOY'
(Other definitions for employ that I've seen before include "Use or take on" , "Use or give job to" , "Take on (staff)" , "Give job to (someone)" , "Utilize" .)