Replace Fusion Drive with Blade SSD

My late 2015 21.5” 4k iMac is equipped with a 1TB Fusion Drive. I believe this is a ~1TB HDD and a 24GB blade SDD. I realize the HDD can be swapped out for a ~500Mbps SATA III SDD. For better efficiency, I was hoping to instead replace the blade SSD with a higher capacity ~3,500Mbps blade SSD. I believe the connection is Apple proprietary. Are there any ways around this like an adapter?