Commuting hard works well. That was pretty much my only prep for the first 10K indoor time trial I did and I've never equalled that performance. I turned that commute into a series of intervals (and was doing it on the heavy bike).

The other comments on endurance (and experienced riders) would hold true, though. I had already done a century (also on a heavy bike).

You might want to figure out some longer routes for when you have time.