Just get a smaller diameter alu tube that fits inside. 1 mm difference between the tubes is enough and practical. The longer you make the sleeve the more tight the fitting becomes especially when the tube is bend slightly like when you do pretensioning the spi pole.

On landyachts were we use masts that are made up out of at least 3 independent alu sections the sleeved overlaps are nearly always 150 mm. (halve a foot) That seems to work well enough.

In your case make the (internal) sleeve permanent on the pole that takes the eyestrap for the bridle strut. The two bolts or monel blind rivets you use for the eyestrap will also secure the sleeve. Smooth out the ends where the breakage occured by sawing off a small piece and VOILA you have a collapsable spinnaker pole, very nice for transporting the boat.

The pole tip wires will keep the front tube secured to the sleeve by compression.

Hell, come to think of it I might even get such a setup myself. Will allow me to remove the snuffer ring a bag and not have them degrade in the weather 6 months a year.

Wouter