I'm trying to see if I can find an easy way to make a 670mm racket (astrox 88s) into 675mm.

I think the most common way is to replace the wooden handle to one that is 5mm longer than the stock grip, but I'm trying to find something easier as i found this too difficult to do alone.

Right now i have some ideas to maybe separate the plastic cap from the handle, put some sort of solid plastic or epoxy and fill it inside the endcap so that it fills around 5mm of height inside the cone, so that when i reattach it onto the wood the length of the racket increases. The blue in the diagram indicates the additional material. If anyone can recommend me a suitable material that is cheap, easy to install, and will remain robust without being damaged, that'll be amazing. And if anyone has any experience doing this and can share some experience on what and what not to do, that's awesome

Are there any other recommendations you guys have for perhaps an even easier method, let me know.