Something like this might be workable - I have no idea if this one is the right size (it was the first one I found) but it slips in - if you were to compress the spring you could possibly insert something like this between the end of the spring and either the bottom spring perch or the strut top mount. I would be careful in the front as the strut top mount has a plate with bearings that allows it to turn and you wouldn't want to accidentally bind that up.
Edit: adding the link:
https://www.summitracing.com/parts/gls-1925