Prepare the MHRB my making a paste with an equal amount of NaOH and water. Then dry and wash with distilled water. Place the basified MHRB in the pipe. Add dry ice. Screw on the end cap. Let the sublimation of the dry ice build up the pressure necessary to liquefy the co2. Let the MHRB soak in the liquid co2 for a while. Slowly open the pressure valve dry ice mixed with spice will come rushing out. Aim it into a large dish. Allow the co2 to sublime completely. Might want to add a release valve on the top to avoid explosions though.

I do not believe the method presented will create supercritical CO2.

You'd probably want a much more involved setup than what you are presenting, and the risks are high (as you acknowledge, you may essentially be building a bomb).

Check out these threads:

Supercritical Gas Extraction of Source Material?
Supercritical CO2 for the Entheogenic Hobbyist

This guy builds custom supercritical CO2 chambers.





Yes, you might want to add one. Don't blow yourself up.

yea chiggels, that diagram isn't an SFE apparatus
and you don't need to add a base for SFE.