Although talking about blisters is kind of gross, I can't imagine there is a runner that doesn't have to deal with them occasionally.
I've been dealing with an especially bad one recently, which I acquired from trying a new type of insole in my running shoes. The best treatment would have been to just take an extra few days away from running, but this week I had a 5k to run (more on that once the official results are posted). To deal with the "mega blister" as best I could during my run, I adopted the following strategy:
1. Two days before the race, I started aggressively treating the area with Aquaphor (good tip, thanks CJ!). I'm not really sure what is inside this stuff that makes it so great, as the only active ingredient is a "skin protectant" but whatever pixie dust they sprinkle in works wonders. It's likely that it would have been mostly healed if I had started using this stuff a few days earlier.
2. I laid off the running for those same two days, which would have been a good idea anyway since I was racing, and swam instead.
3. Before the race I coated the area with two layers of a generic liquid bandage. Then I covered the area in body glide to hopefully keep as much friction as possible away from the area.
4. After the run I removed the liquid bandage and reapplied the Aquaphor.
Anyway, this is a strategy I'd use again if I had to. If you have to run/cycle with a blister I'd recommend giving this a try.