Identify where you want the joints. Remember to make the tip section longer than the remaining sections (each will have a 10cm spiggot
Cut the rod into the sections, do not use a saw, this tears the mat of the carbon and then splits the blank. Use the sharp edge of a file and cut it around
Now using lengths of blank of similar profile, insert the blank (spiggot material) into the blank to be converted. (mark where it seats against the blank to be converted - now cut the spiggot blank 8cm above where it seats and 12cm below where it seats. now to reinforce the spiggot slide the remaining section into the spiggot and epoxy it into place, making at least a double wall, possibly 3 walls.
Now pass the spiggot into the new section from below and epoxy that into place (re-inforce the blank being modified or you might just split it and if you do you will have to throw the rod away.
Do the same procedure on the mid and butt section. this requires removing the reel seat assembly (ram it out or cut the blank 12cm above reel seat and remove the butting. Once the spiggot is in place re-build the reel assembly.
Now on each spiggot joint make at least a 3cm bind with D cotton to ensure the new sections don't split when under load.
Best solution find a buyer for a 1 piece and buy a 3 piece blank and assemble it yourself.