Modifying iCal drawer fields?

I’m new to scripting, and am wondering if it’s possible to change and add pre-defined fields to the “more info” drawer in iCal. I want to use iCal as a training log app, and want to be able to quickly enter a workout time in a new “Time” field, for example.

I have my training schedule as a calendar in iCal, and would like to be able to enter data from that workout once I’ve performed the workout. I’m a cyclist, so the data will be heart rate averages, maximums, ride distance, time length, etc.

Any insight is much appreciated.