That’s an interesting conundrum. Let me see if I got it right:
1. Your product options are actually weight instead of individual quantities;
2. The client chooses a 1lb option but it’s actually heavier due to the packaging/ice;
Can’t you simply calculate how much ice per pound is used and set that overall weight for that option?
If I’m wrong in my assumptions, please send me a link to the site by email so I can have a better idea of what the issue is. vinny [at] usestrict [dot] net