You can locate your DVR and PTZ keyboard next to each other, splice them right there, and then run a single long wire to the camera.
I probably wouldn't screw the keyboard wire into the back of the dvr along with the camera. But, that could work.
The thing with the electrical signal is it will travel OUT of the DVR and go down both wires - one to the camera and one to the keyboard. (and vice versa for the keyboard and the camera.) If you run into problems with the keyboard/dvr/camera not working with this splice then you should install diodes on the keyboard and/or dvr wires - be sure to orient them in the right direction because diodes are designed to allow electrical current to flow in one direction but not the other. The diodes will prevent the DVR from sending its signal the Keyboard (for example).
This might only be a problem for cheap electronics though.
