To be honest these drills won't have a great impact in getting you much faster before the race but it must be psychologically satisfying to get in the water and do some laps.
Front Sculling and Underwater Recovery:Both techniques I give to my athletes to improve the catch phase of the freestyle stroke:
One Arm Freestyle (with the injured arm by the side):
Kick and Body Position Drills:
While the gains in fitness might be limited you can definitely, with a bit of persistence, maintain and even improve your feel of the water with these drills.
Let me know your experience if you've ever had a broken collar bone.