I found this tip on HPA Mooney Cookup in the Indoor section. 

The idea is to keep the rubber motor from flopping around as it unwinds.  Works with braided and unbraided motors.  Some use two chokes depending on length of the fuselage and length of hook to peg. 
RalphS also added this quote: "Just out of interest the Cameron 1943 Flight Cup Winner (Aeromodeller November 1944) used the same idea.  It has two formers (located under the wing) each with a small circular hole.  In the article Ivan Cameron says to give the edges of the holes plenty of banana oil, sand and polish smooth. When I used to go to the Wirral I would visit Ivan and once asked him what the holes were for?"
He said "to stop the motor bouncing about wasting energy".
HPA link
Gonna have to check into this and add a few chokes to my planes in the future.
Sky9pilot