Physically this should be possible but I've never seen an SSD that allows it. I think very very few customers would use it, but I'm still a little surprised no vendor offers it.
I suspect it's heavily firmware-dependent, but I do wonder if taking a TLC drive and partitioning it to 1/3 of its advertised capacity will keep all the blocks in SLC mode, since the firmware, if it's behaving reasonably, should try to use SLC as much as possible just for the speed benefit that brings, and only start converting blocks to MLC/TLC once all the blocks have already been used in SLC mode.
Coincidentally I did some research on this topic the other day and I couldn't find any SSD model with unlimited SLC cache. They all have fairly low limits like 10% of overall capacity.