I think the easiest thing, until you know how weight lifting is going to affect your bicycling, would be to commute by car on lifting days. I find it's easiest to reduce reps but increase weight.

If you get to a point where you feel like you have sufficient energy after a workout, then try adding bicycling too. If you haven't been lifting in a while, DOMS may make it hard for you to bike the next day, too.

Or, if you have a backup (ie, someone who can pick you up if you completely run out of juice) you could try biking and lifting together.