Copy the SDCX.DSK file to the root of your SD card and rename it to SDCEXP.DSK.

Create or modify your startup.cfg file at the root of your SD card to mount the
SDCEXP.DSK disk in drive 0 or 1 at startup. To do so, add the line #=SDCEXP.DSK
where # is the drive number. Example:

0=SDCEXP.DSK

With this setup you can now use the EXP command to run SDCX.