Step 1: Requirements and Getting Started
1 Mountain bike inner tube
Puncture repair kit (optional)
Measure the length of your keyboard and cut the inner tube slightly longer making sure you have the valve in the length of tube to be used, exact measurements aren't needed, I just laid the inner tube over the keyboard and then added a few inches.
Step 2: Sealing the Ends
Clean the inside of the tube and run some glue from the puncture repair kit around the inside where the cable ties will grip it, to give a good seal. Personally I've not needed to do this as the friction seal from the cable ties sees to be doing just fine.
Step 3: Finishing Off and Improvements
Once you are sure the seal is good, take the short lenth of tube sticking out from the cable ties and fold it back on itself to hide the ties. This is alot easier if you deflate the tube first.
Place the tube under the rear of your keyboard and adjust the air pressure until you have a comfortable tilt.
I will probably replace the air with sand as that should improve the "moldability" of the lifter without having to mess around getting the air pressure exact, and I'll be able to use a length of tube without the valve.