Things that I have found help me with specifically wrist locks, but some of which are adaptable to other forms of practice as well.
Grab a Partner for an Extra Day
This is really the best option, but also logistically the most difficult. Talk to the other students in your class and see if one of the more experienced ones would be willing to add an extra day of practice every week or so. I understand that this is side-stepping the problem slightly (since you asked about training outside of class without a partner, and it is an answer on training outside of class but still with a partner), but it really is the best form of practice since no tool I am aware of can properly simulate not just the joints but how the body moves when put into a lock.
I recommend avoiding using a friend or significant other unless they also have training. You really don't want to accidentally injure your significant other, which is easy to do if they don't have some experience in the locks themselves.
In my hapkido class we practice a variety of wrist stretches where we simulate many of the basic wrist-lock motions. So for example:
- Hold up your left arm so that your elbow is level with your shoulder, palm down, pointing forward.
- Turn the elbow inward 90 degrees, so that your fingertips are pointing toward the wall on your right.
- Rotate your wrist, so that the palm is facing toward the wall directly in front of you.
- Turn your wrist so that it forms a 90º angle with your forearm, fingertips pointing toward the front wall, palm toward the wall on your left.
- Move your wrist over in its current position so that it is directly on your center line.
- Take your right hand and place it against your left hand. Thumb on top, fingertips underneath and in front of the thumb.
- Gently push in and pull up toward your face.
- Hold that for a little while, then release, repeat with your right hand.
You can build an entire set of these. They have three advantages:
- They simulate the direction your wrist should turn for a lock, stretching and strengthening your wrist against these techniques.
- They train you in the mechanics of the locks and can help practice it when you do not have an available partner. It tells you a lot about the mechanics of the lock, which then will translate into your actual practice.
- It lets you experiment on just the wrist mechanics without risking injury on a partner.
Some of the key parts of getting locks to go on correctly are actually independent of practicing the locks themselves. Things such as:
- Moving your feet correctly, without sloppy stances (or as we like to say, "sloppy stances make sloppy technique").
- Sinking your weight.
These things can be practiced independently of actually doing the lock, but can provide a dramatic improvement to your execution. You can also easily practice these on your own, so take the opportunity when you aren't in class to practice these ancillary components. That way you can spend more time in class productively studying the locks themselves.