Jumping pullups (use as much leg push as needed, lower slowly . . . this really keeps the cardio going in a WOD like Fran)

Pure negatives (climb to top position using whatever means necessary, chair, bench, whatever, then lower slowly)
 

Assisted Pullups: use a Gravitron machine (if you're lucky enough to have access to one), or, even better, a human spotter to give you a lift. Bend your legs at the knees so that the tops of your feet are facing down, have the spotter support you there to provide some lift.
 

Assisted pullups 2: Get a large elastic band (surgical tubing works great), loop over the bar, step in it to provide some lift

Reduced load pullups: Suspend a bar (maybe an Olympic bar for weights?) at a height less than overhead . . . maybe about chest high . . . get underneath it with you legs in front and body straight . . . do "pullups" with your legs still on the ground, supporting part of your weight . .

All of these have the advantage that they are neurologically more valuable than the fairly un-natural motion of locking your knees under a pad and moving just your arms . . . in all of these, your arms are going to be drawing your whole body up . . . you will progress toward "full" pullups faster.
But yes, you can do pull-downs, and doing those are infinitely better than skipping this workout.
Courtesy of Dave Wood