Many times the vinyl tank tracks that come with 1/72 scale kits are too short to readily fit around idlers, road wheels and drive sprockets. Recently, I used a heat lamp, a piece of cardboard, and a paint stick to stretch the beige vinyl tracks from a Dragon T34/76 1/72 kit (see first pic). Amazon boxes work well for this because they are thin and sturdy. 1) Staple a paint mixing stick to the cardboard (this stiffens the cardboard which will warp under heat without the stick); 2) Staple one end of the track to the cardboard; 3) Stretch the track carefully (usually 2 or 3 links are enough) then staple the stretched end to the cardboard; 4) using a heat lamp at a safe distance from the treads (start a foot away then move in slowly; too close and the tread will break), apply heat 'til tread begins to sag, being certain to move the lamp every 15 seconds or so from left to right because the heat is most intense at the center of the lamp; 5) allow to cool. Picture 2 is an image of an un-stretched track next to the stretched one.
If anyone tries this on glossy black vinyl tracks, let me know how it comes out.