Is it possible to break the fusion drive from my mac mini?

While its quite easy to break the fusion drive set How to split up a Fusion Drive.

A SSD RAID set won't work terribly well here ;-{

The problem is the two ports are not the same data rate. You have a SATA III (6.0 Gb/s / 750 MB/s) and a PCIe x2 (8.0 Gb/s / 1 GB/s) interface in this system. Now remember these are the Theoretical Maximum Throughputs. Now lets look at what is more likely the case: SATA III - 4.8 Gb/s (600 MB/s) & PCIe - 6.4 Gb/s (800 MB/s). Still not really a match which is what you need when doing RAID.

You have a few choices here. If your blade SSD is on the small side you could try getting a larger unit and then use your HD for holding your data (doc's, music, vids, etc...) Presently Apple is the only source for the custom SSD. OWC has been teasing us for a good 3 months on their web site: Mac Mini SSD upgrades sorry to say still nothing yet. Getting the correct SSD is just impossible from eBay or other sources. There are quite a few scammers out there telling you they have it, then they don't or they give you the wrong type (M.2).

Your other option here is to pull the blade SSD out and just use the SATA port with a 2.5" SSD. Then, use an external Thunderbolt drive for your data.