Bobby keeps preparing a way for Jack, say (7,4)
I believe the answer is:
playing card
'jack say' is the definition.
(I know that jack is a type of court card)
'bobby keeps preparing a way for' is the wordplay.
'bobby' becomes 'PC'.
'keeps' indicates putting letters inside.
'preparing' becomes 'laying' (laying is a kind of preparing).
'a way for' becomes 'ard' (I can't justify this - if you can you should give a lot more credence to this answer).
'pc' placed around 'laying' is 'playingc'.
'playingc'+'ard'='PLAYING-CARD'
(Other definitions for playing card that I've seen before include "heart, say" , "One of the pack" .)