There are a couple useful tricks you can use.
For fretting hand exercises, you can pull your right arm across your chest to the left side of your body to approximately the location that your (bass) neck would be and use your wrist/upper forearm as your neck. You can just imagine the location of the frets and practice scale patterns, arpeggios, etc. I first used this idea when trying to explain a guitar chord shape to a friend and I actually drew frets and strings on my arm with a Sharpie. Haha.
A useful trick for plucking hand exercises is to either use the edge of a belt buckle (I had a great one shaped like a combo amp that was just about the thickness of an "A" string) or alternatively you can use the edge of a table that you can strike your fingers across while providing resistance. If it's solid then you can choose how much resistance you want by simply digging in a little deeper. Great for speed, strength, and rhythm exercises.