What's-his-name is lanky, sticky fellow (12)
I believe the answer is:
thingummybob
'what's-his-name' is the definition.
'lanky sticky fellow' is the wordplay.
'lanky' becomes 'thin' ('thin' can be similar in meaning to 'lanky').
'sticky' becomes 'gummy' ('gummy' can be a synonym of 'sticky').
'fellow' becomes 'bob'.
'thin'+'gummy'+'bob'='THINGUMMYBOB'
'is' is the link.
(Other definitions for thingummybob that I've seen before include "gizmo" , "Oojamaflip" .)