Strata law doesn’t anticpate acts of philanthropy (with strings) so this may be as good as you’ll get.
The casual approach I suggested was before realising the strings attached. I would be philosophically opposed to that. If something is worth doing to improve the common property then the OC should decide and pay for it.
There is a ‘slippery slope’ argument against letting people with more money get to have disproportionately more say than their single vote about what happens to the common property.
In our OC we have a couple of good quality park benches that an owner salvaged for nothing, cleaned up, restored, and put in places on our grounds that are nice for sitting and contemplating the view. Nobody has objected or even asked where they came from but the donor understands that if ever the OC decided they should not be there, he would take them away. If he had demanded money for them, it would have been very different.