This is my predicament as well. I already run 5 times a week in my dinner hour at work but want to train for longer distances (ultra's). This means that to get more miles in I need to change 2 dinner hour runs with 2 longer evening runs. The problem is that I also want to keep the gym up and the days I usually go to the gym are the only days I can do my long midweek runs (family commitments etc).
What I've decided for the moment is to do the gym work at home instead. I wasn't trying to bulk up as such just to tone up so I can do pretty much the same routines with the limited equipment I have at home, such as gym ball, resistance bands, dumbells and abb wheel. I just need a little more self discipline to actually do the work. I now do the resistance training on Monday and Thursday night.
Hope this helps