If you did a full BFL workout to failure, you'd be exhausted, overtrained, and probably see less results than if you followed the plan as written. Being a chronic over-achiever type, I tried that when I did my first BFL challenge. I lasted 6 weeks doing that.
If you really want to lift more frequently and see more dramatic results, here's the change I'd suggest: break Upper Body into 2 days so that You are really lifting a 3 day
split and do cardio on all days except lower Body and rest day.
Here are a couple of possibilities:
Week 1
Day1 (Upper): Chest and Shoulders
Day2 (Upper): Back, biceps, triceps
Day3 (Lower): Legs and abs
Day4 (Upper): same as day 1
Day5 (Upper): same as day 2)
Day 6 : Cardio only - or put day 6 between day 3 and 4
Day 7: rest
Week 2
Day 1(Lower): Legs and abs
Day 2 (Upper): Chest and Shoulders
Day 3 (Upper): Back, biceps, triceps
Day 4: cardio only or use as day 6
Day 5(Lower): Legs and abs
Day 6:cardio only
Upper can be
split a couple of ways-1)back and shoulders, 2) chest, bi's tri's
3) push-pull : chest, tri's and shoulders (push), back and bi's (pull).
It's still a lot of lifting. If you do this, I'd suggest changing to a lighter workout week somewhere near week 8-10 and do maybe 3 full body workouts, then go back to your regularly scheduled
split
Or as Ilene suggested, finish out as written, and see how it goes. A lot of people really don't see the kind of results they were expecting until at least weeks 8-10. Give yourself some time
Mel