My girlfriend did her first metric century last year and she didn't do a lot of special training aside from riding her regular commuting route (5 miles each way) and doing a 30 mile trip out to 'burbs.
I think that if you're regularly doing a 22 mile round trip commute, your fitness is probably at a decent level for a metric. Your plan of doing a 40 miler the weekend before that should be good prep.
The one thing to be mindful when being on your bike for multiple hours is to eat and drink properly. 250 calories per hour (or two long Fig Newton cookies) and at least 500 ml of fluid, I'd say. Eat before you're hungry, drink before you're thirsty and you'll be surprised with how far you can go.