OH,,,
I misunderstood.. find the thinnest lightest paper you can (like adding machine paper, comes in a roll about 2" wide, get it at an office supply store) and just roll it into as long of a tube as you need. Once you roll it out tape the ends or and or tack glue the tube with a little CA along its length to make it hold its shape and then run your servo extensions through it... This is a 2 minute project.

OR, you can just use clear packing tape and tape the extensions down tight to the wall of the fuselage. They wont move at all and it should last forever. This is what I do when I have tail servos... Its very light, works really well and will last forever..... You just have to be patient and get creative with long balsa sticks and tape to get it back in there and stick it down. Most pattern guys are creative at working with long spare balsa sticks or dowels and using them to find ways to work way back inside of the fuselage.