Hmmm, that post was quite some time ago... many beers have gone by since then...
I believe that some dealers still cary it, and or there are other's that have said to use plumbers puddy, and or other materials such as this...
If you can find something like this, that is flexable, water resistant, and you can mold it into a rope type shape (much like Plumbers puddy) you should be set.
I hope to pull my kicks off again soon to add stock speakers and grills (on new speakers in the stock location!) and to paint them etc... so I too will be doing this soon!