I would pass on that technique. Most ice packs I have seen have weird textured surfaces. There is also embossed lettering on them too. The likelyhood of actually sanitizing all though nooks and crannies is low.
Unless you are talking about sourcing some uber smooth surfaced bottles and freezing them it might be worth a try on a few brews.
I suggest you try stirring the wort. Put a good spoon in there right before you start chilling. Once the wort gets down to 90F start stirring every once and a while to circulate the wort around the chiller. That should help.
Keep in mind too that if your ground water is only 60F it will take a long time no matter what you do to stir.
Look into using a prechiller to get that chill water down to 40-45F.
I use a pump to recirc the wort while using an IC (whirlpool chilling, not my idea. I take no credit for it.) I go from boiling to 65F in 40 minutes this time of year. In the summer I set up a prechiller and get about the same rate.
Sound though like you are chilling really fast already. Compared to most people, I think you are already using much less water than everyone else. If its a big concern you could slow the flow and maybe add 10 more minutes to the chill, but save on water.