If you are able to ride 4 days per week for your commute, you can definitely work in some quality training. The wonderful thing about your body is that it doesn't care if you are on your race bike or commuter bike, your lungs and quads can't tell! You just need to build a training program into your commute. Start adding some intervals and hill repeats. Leave room to build so each week gets a little harder and a little harder a you are building. Leave plenty of time for recovery days and recovery weeks. You other limiter might be bike handling skills, so make sure to get out at least one day a week and do nothing but work on 'cross skills: mounts, dismounts, off-camber turns, run-ups, etc. If you have clinics in your area like we have in Portland, try to attend. Good luck out there!

RC