I simply made a start image [LEFT] and a right image [RIGHT]. Then I made a middle image and that image extends depending on the amount of popularity, activity etc.. I'll try and make a little example here
[L][---------------BG][R]
L= The left image

------ = The image for the tube. Extends depending on pop/actvity etc..

BG = the background image so that it has a default size..
[R] = Right image
I would prefer not to post the code, as I don't want people using the same images as myself