I did a similar thing with the Harris pole,
I removed the largest screw handle from a 2nd pole glued this to the but end of the 1st pole,
then on the 2nd pole, the top section ( thin bit ) cut off all fittings then covered it with scilicon and slid this into the middle section of the 2nd pole,
Keep up with me!!
When set the glued section of the 2nd pole slips into the glued screw fitting on the but end of the first pole, max length is approx 26-28 foot
However the only thing is,
it is a bit whippy when fully extended
But not bad for the few jobs i have at that height.
SL-X later in the year hopefully
Tom