Put on wrapping paper, which is to prove tedious (4,2)
I believe the answer is:
drag on
'is to prove tedious' is the definition.
(to drag on is to become tedious)
'put on wrapping paper' is the wordplay.
'put on' becomes 'don' (synonyms).
'wrapping' indicates putting letters inside.
'paper' becomes 'rag' (rag is a kind of paper).
'don' enclosing 'rag' is 'DRAG ON'.
'which' is the link.
(Other definitions for drag on that I've seen before include "Proceed for an extended period of time" , "Continue interminably" .)