While CRAM is indeed much smaller than BAM, its primary benefit is when using aligned data so you can use a reference sequence (whether external or embedded). It does however still work without a reference.
I wouldn't recommend creating a fake reference just to get it to swallow things. You shouldn't need -T at all as with unaligned data there are no references to compare against anyway. Also note for aligned data, if you really need to, there is a way to enable referenceless encoding using "--output-fmt-option no_ref=1", although it's not going to be hugely beneficial.
Incidentally for FASTQ compression things have hotted up in recent years and there are far better tools out there, albeit due to doing mini denovo-assemblies (either by bloom-filter, graphs, or kmer counting strategies). They're often very CPU and memory hungry, but obviously yield far smaller files than CRAM as they're essentially doing reference-based compression with the reference computed on the fly.
FaStore, Spring and FQSqueezer are modern tools for this process.