Re-shaping a glass slide??

About a year ago a friend gave me a slide they bought that didn't fit their bong. It didn't fit mine either, so its been sitting on a shelf in my closet ever since...

Now I dont even really know what made me remember that it was sitting there, but it occured to me the other day to try and reshape the stem of the slide a little bit. I'm talking about like a millimeter or two, nothing drastic, and it'll fit like a glove. Now, I have a torch and everything, and I remember some of the basics of heating and reshaping glass from high school science class, but I was wondering if anyone could give me some idea of a good technique. I'm thinking that if I heat up the stem and roll it gently between a couple of small blocks of wood that may work. I got the thing for free from a friend who got it pretty cheap some place or another, and I cant find anyone who has a bong that it will fit, so I'm not gonna be too devastated about it if it breaks. But I'd like to see if I can get this to work, its a nice looking slide that goes well with my bong... Thanks for any input...