volume spacer alternative in shock

hello all suspension feckers. I have Xfusion vector air shock – great shock with plenty adjustability . But i wonder what can i put in to add some more progresivity. Xfusion does not offer air volume kit similar to Fox ,so I am left wondering if there is some DIY reliable alternative.
please dont tell me to add suspension oil – works only temporarily as it will leak through seals…

I thought the common trick was to partially pack the air can with grease to take up a little extra volume..

Or cut a strip of closed cell foam or a bit of mousemat.

Slices of plastic wine cork.

thanks guys. i will try the foam