It is not recommended that you add additional strength training workouts to the BuiltLean Transformation Program. The workouts are specifically designed in a way that creates maximum muscle stimulation in a very short period of time. Any more lifting could actually hurt your results.
If you want to add more activity to your weeks, you can do more cardio, or perform active rest on the days that you are not lifting.
On non-strength circuit days, consider doing a walking, jogging, swimming, or rowing for 30-45 minutes. Other forms of activity like sports, yoga, or foam rolling is great as well.
The most important thing is to follow the BuiltLean workout program, and anything extra you do on your own should be focused on helping your muscles recover.