3 weeks is plenty of time, especially since you are already in good running shape.
I have only done it once, but finding the right delivery system (beer or can) and getting the beer to the right temperature seem to me to be big keys. I had major foam issues, which made finishing the beers a pain in the ass and made the last half of the race pretty damn uncomfortable.
I would submit that you should be able to do the actual running part at mile race pace (or faster) given that you are getting a little break in between - the question is, will that be a 10-15 second break or will it be a 40-50 second break.
You can probably practice every day by having a beer ready at your door and finishing your normal run with a 30-60 second pick up, crushing the beer, then doing another 30-60 second pick up. Maybe do one workout where you do 8 x 400 on modest rest, with the last 2-3 reps being preceded by a beer.