It's simple. We've already warned Prelate Souf and Assassin Flamb about the dangerous blood-nannies.
We set up the teraport cage under the pretense of "containment."
When the clone is done, we make the switch. Any observable power drain can be ascribed to "zapping airborne nanites."
Okaaay. . . but does the teraport cage provide any actual containment?
Well, not as such, no.