Just some thoughts...
Boot from an EXTERNAL MAC DRIVE.
Scrounge up a copy of Drive Genius version 2 or 3.
Now, do this:
1. Use disk utility to do a "quick erase" on each drive
then
2. Use DG to "erase free space" on each drive (i.e., write zeros to the free space).
Actually, once you "un-fuse" a fusion drive, all the connections to the data on the formerly fused drive are lost, and probably unrecoverable to 99.9% of the people out there.
Alternative:
1. Use disk utility to do a secure erase on the HDD.
2. DU won't do a secure erase on the SSD (at least, I don't believe it will, I could be wrong).
If not, don't worry about it. The chances of getting data from an SSD that was formerly part of a fusion drive -- now UN-fused -- are almost zero.