That would definitely make installing a slider a whole lot easier, but I came across another trick for installing a slider. A can't find the link right now, so I will briefly describe the technique (perhaps someone has posted it here before?). It makes adding sliders so much easier!
Start by separating a few inches of your zipper at the end you want to install the slider. Next, take a few inches of masking tape, scotch tape or whatever kind of tape you have handy. Use the tape to 'extend' the fabric portion of the zipper tape to make a 'pull tab' of sorts. You do this on both halves of the zipper. You can then feed the slider down the tape to the start of the zipper. The tape doesn't really guide the slider, but it does give you something to pull on for leverage as the slider meets the zipper teeth.
Edit: Wow, that explanation was terrible! Here's a link to a tutorial with pics: http://glass-beach.blogspot.com/2007...pper-pull.html