Isn't calibration carried out at the monitor these days? That is, during setting up with an actual patient?
I'm not sure that anything you can do away from a patient would be any improvement on that (because that way you are testing the complete circuit as used in a "live" situation). As you know, the PiCCO patient set up (tubing etc.) is relatively complex.
Back in the "old days" we used to calibrate the transducers of invasive BP systems separately. That is is, just the monitor and the transducer (via its cable). Different than Cardiac Output, I know. There were a few testers (Bio-Tek et al) that could inject a signal into the monitor via a suitable cable (but that, of course, only checked the monitor).
Which monitors are you using? And are the nurses complaining?
