I don't have an answer, I'm afraid, but I am looking for the same thing. Have come to a V60 from a Skoda Superb and that had a solid plastic panel across each recess which gave a decent amount of storage for small items.
If there is an "official" Volvo part, it should apparently be on the Accessories website, however, there does not seem to be anything available for the SPA V60 or V90. Searching across all models:
https://www.volvocars.com/uk/accesso...t&pageNumber=1
Brings up 2 "Pocket net kits", one £95 the other £145, which seems pretty scandalous to me given that I have seen similar nets on ebay for under £10.
Something like this might do the trick:
https://www.ebay.co.uk/itm/Car-Trunk...-/223670477003
In fact, for £5.50 delivered I might just treat myself.