I know this thread has been dead for a while, but I have found a nice(ish) solution.
I have an offline assignment for each week of the term that the students are in Labs. the assignment has an Outcome attached to it. The outcome is based on a scale that is a complete list of the experiments that students undergo.
This meens that when I come to mark the work in the students lab books I can note the mark and choose the experiment they did that week from the outcome drop down...
Obviously this is a slightly odd way to use outcomes and I have to exaplain to the student to ignore the percentage grade that is attached to the outcome. But I now have a grade book that records what experiment each student does each week