Technically we do not supply 'Extensions' for the CLX, SLX & Super-Max range of poles. However we do supply a complete range of spare sections for these poles, which many clients have bought and are using as extensions.
If you decide to do this then we would recommended as 'brianbarber' has done. This would entail removing the insulated handle section with end cap and then replacing this section with a mid-section tube and any others below it to the height required. This maintains the full structural integrity of the pole design, because the handle section is less rigid than the other sections due to its insulated layer. The handle section can also be slightly wider than a standard mid-section tube, due to the insulated layer. Because of this we do not guarantee compatibility with sections added to the handle section.
For example - If you currently have an SL-X30 (6 sections) and wanted to add 2 sections (10ft) to the pole we would recommend buying a new section 6, Section 7 & Handle Section 8. To fit this you would undo the lever assembly and remove from the No.6 section clamp then open the jaws of the clamp and slide the handle section off of the pole past the joint stop. Then take the new sections, remove lever arm assembly, open clamp jaws and slide onto the section 5 of the pole. Re-assemble the lever assembly and the pole is now extended by two extra sections (about 40ft).
Whatever is added or taken away from a pole we would always recommend an insulated handle section is left on the pole for safety.