I also have a SSD in the WWAN-port (7490) and it is accessable, if I load the BIOS-defaults. On next boot the BIOS seems to overwrite automatically the settings and the drive is gone. But it appears each time I load the defaults (but only for one boot). In my 7440 this constellation worked, in the 7490 not.
I now try the CCTK and hope I find a setting, which makes it permanently visible.
I think, it should be supported by Dell as a second harddrive, many of our users want to seperate the data physicalls from the system.