Sundays and Wednesdays

My scheduled rest days from exercising are Sundays and Wednesdays.  It is becoming increasingly more difficult for me to not exercise two days a week.  These two days are prescribed in the half marathon training plan I am following.  I am going to have to find something I can do which gives my legs a rest on these two days but still gives me a good work out.  I have been thinking about starting to use the Bowflex again.  Now may be the time.  Currently, I have been biking for at least and hour Monday, Tuesday, Thursday, and Friday.  I have been running Monday, and Thursday with a long run on Saturday morning.  I think I will start using the Bowflex on Wednesdays, Fridays and Sundays.  I am not sure however, that an upper body workout on the Bowflex will give me the exercise "fix" that my body now craves daily for the two days per week that I am not running or cycling.