David,
as you know I'm not in the same league as those guys, but I pushed it out to 30K a couple of weeks ago ahead of a race and I need to get in some more long-ish ones in the weeks ahead, so I'm interested.
I've been scavenging those 500ml Coke bottles from people who drink the stuff at work, and running with one of those full of electrolyte in my hand. When it's empty, I just dump it in a waste bin, or in someone's recycling bin - round here, they're blue.
In the hottest weather, I found that wasn't enough and begged water from strangers in their gardens.
Some folk I know go round the morning or the evening before by bike, and stash bottles in hedges. I was thinking of trying that. It might work quite well with the disposable scavenged bottle approach. In fact I meant to do that today, but I didn't get going early enough
I also carry a couple of Isogel sachets, as they claim not to need as much water to go with them, but I don't really know if that makes sense given I am presumably just carrying the extra water in the gel anyway.
Interested to hear other's approaches.