I found an assist-esque setting to make extending hypers and supers easier! There's an 'extended variant' to turn off the dash regain cooldown, so that you don't have to wait on the ground for a bit before pressing jump. This means that all unextended hypers and supers become extended (i.e. you regain your dash after the technique).

You have to download the Extended Variants mod. Then, in Mod Settings, go to Extended Variants > movement > disable dash cooldown, and toggle it to ON.

Having instant extended tech will probably mess up your muscle memory for extended hypers or supers, so use it with care!

On a separate note, you can also try wavedashing.

A good practice map for extended hypers is 'Starry Ruins' from the Strawberry Jam mod, you can find it in the Advanced lobby. It's a short map but the last two rooms require doing extended hypers in a row, on small, falling platforms.