The GWT editor has the TM merge feature which can copy the top TM match result into 1 page of translations.
auto-fill can be toggled on and off easily
the top suggestion match is automatically copied to a phrase when the phrase becomes selected, as long as its match percentage is high enough
text is copied to the editor window, but not saved anywhere until the translator saves
check the existing TM merge code for the threshold options
keep current rules from TM merge about whether to copy when there is already a translation present
the UI indicates that a match was copied
e.g. "copied 98% match"
indication includes the match colour (e.g. dark-blue for imported TM, green for translated, etc., see the middle bar of the suggestion panel)
animate in some way to briefly catch the eye. May animate as if emerging from the suggestion icon in the phrase footer (as long as it looks good, implement then have design assessment).