Anaerobic Capacity workouts for an 800 meter runner need not be different than for a 1500 meter runner. You simply do workouts to maximize your anaerobic work capacity, period, whether you are running the 800 or the marathon.
It should only take about 6 weeks to maximize your AWC if you are already fit.
How might I suggest you do it? Seriously, you go all-out from the beginning of the rep and hold it until your form starts to go to hell. Maybe that'll take you 200 meters, maybe 600, but expect to run into a wall around 2-300 meters if you are truly going all-out. Full recovery. Walk for about 10 minutes in between. You aren't out there to train your aerobic system.
Not a lot of time in the grand scheme need be spent here, as the aerobic system takes MUCH more time to maximize.
Anaerobic contribution for a 2:00 all-out effort, for an aerobically fit runner, is likely to fall between 25-45%. That includes the super aerobically fit athlete with poor anaerobic capacity, to the aerobically average runner with a world class anaerobic capacity.
So, it's obviously important to maximize for the middle distance events, but again, it's something that only takes 4-8 weeks really.