I believe that double-hashing is "equivalent" to single-hashing. See this issue: https://github.com/ipfs/refs-denylists-dmca/issues/2

There are some ways of doing it, depending on exactly what your threat model is, but I think it's risky in general. Right now this is just in the planning stages, but I want to have submitting URLs be a manual button click for each download, and also provide an option to use a local copy of the database (so that all lookups would be completely private).