Charge added to bill for buttonhole (6)
I believe the answer is:
accost
'buttonhole' is the definition.
(both can mean to detain in conversation)
'charge added to bill' is the wordplay.
'charge' becomes 'cost' (I've seen this before).
'added to' means one lot of letters go next to another.
'bill' becomes 'ac' (short for account).
'cost' put after 'ac' is 'ACCOST'.
'for' is the link.
(Other definitions for accost that I've seen before include "Approach boldly or insolently" , "Stop and pester" , "Approach or confront boldly" , "Approach boldly or impudently" , "Approach or hail boldly" .)