Learning to run twice a day

Running will always be my first love. As I have said before, what I lack in speed, I make up for in enthusiasm! Most times when I go for a run, it is a fairly neutral experience. Sometimes though, I hit that sweet spot and am reminded of what a wonderful thing this running business is.
Last year, I spent some time thinking about what it would be like to run twice a day. Although it seemed like a great idea, it also seemed highly unfeasible. It seemed as though I needed to conserve all my energy for a "good" run. On alternate mornings I would do some circuits, and with time I eventually incorporated bricks into my workout.
A few days ago, a colleague mentioned that she wanted to get a bit fitter. We decided to go running for half an hour twice a week, during lunch. Irache and I started last Tuesday, on a baking hot day! We started off with a brisk walk, then ran for a bit, then walked some more and ran another bit. It was a gorgeous day and everyone was out running along the Charles River. The Boston skyline was magnificent to behold, and it felt good to be outside.
It was quite a rushed business having a shower, getting lunch and being back at our desks, but we managed it in all of 50 minutes!
We went out on Friday afternoon too. The weather was considerably cooler, and it was pleasant to run outside. We ran a bit more and went further. On the way back though, we walked briskly and ran a lot less, as we were chatting a bit. Today we did not go out as both of us were swamped with work. Friday is a double session though!
The good thing about running with Irache, is that I have the opportunity to slowly start building a second running session into my day. Furthermore, it is quite fun to run with someone else in the middle of the day. Running in hot weather is something that I cannot do - I hate it. But if the body can adapt to anything, I am keen to see if this might happen. We are almost at the end of summer, but I am sure we still have a few hot days in store.
There is a great article in the July issue of Runner's World entitled Double Duty, which recommends incorporating 2 days a week, of 20 minutes, whilst dropping the length of your main run by 10-15 minutes. When you feel strong enough, bring your main run back to its original level and extend the extra run up to 40 minutes. Most importantly they recommend a 4 hour rest interval between sessions. After the first run consume at least 500 calories and drink!
The article concludes by recommending the following paired workouts:

A.M.: 3 to 4 at easy aerobic base pace
P.M.: Interval workout (e.g., 6 x 800)
PAYOFF: Provides extra aerobic work without fatigue, gets blood flowing through muscles

A.M.: 4 to 5 miles at easy aerobic base pace
P.M.:4 to 8 miles at a conversational pace
PAYOFF: Improves running economy, boosts weekly mileage, and provides a good fitness base

A.M.: Long run; or 5-K or 10-K race
P.M.: 2 to 3 miles at a conversational pace
PAYOFF: Increases blood flow to muscles, flushes waste from muscles, and speeds recovery