Another option is to remap an embedded keypad to the left side. For the past 2 years, I have used this setup on my Kinesis Advantage.
I have an extra enter key where 'b' is (the left thumb cluster could be remapped though), and an extra '0' on the key beneath 'x', and use both when I must use the mouse. I prefer to use the default embedded '0' and enter in the right thumb cluster. I use a foot pedal to toggle back to the non-embedded layer when I need to use letters.
If remapping to the left side on a Kinesis, you retain numpad navigation, i.e. numlock off, so you can have navigation on the left if you want it. This actually puts pgdn and pgup in better positions.
Prior to using the Kinesis, I used Autohotkeys to remap these keys, but IT locked the computer down and eliminated Autohotkeys