Take the 1st LO output (2 - 4.4 GHz) on the front panel into the LO port of a high-quality microwave mixer, like a M/A-Com or Watkins-Johnson M1H.
Apply a 2.050 GHz signal from an external signal generator on the RF port of the mixer, around -10 to 0 dBm.
The IF output of the mixer will then track the HP8569 in the 0.01 - 1.8 GHz setting. There should be a 3 dB attenuator pad on the IF output of the mixer.
Connect the IF output from the mixer to the RF input of the HP8569B to get your baseline response.
Store that response in Trace B by using "STORE VIEW" or "STORE BLANK."
Connect up your device to test, then press "INP-B->A" to normalize the response.
On the 1.7 to 4.1 GHz setting, use the same mixer but put a 321.4 MHz signal on the IF port and take the output from the RF port.
The other ranges are based on harmonics of the LO, so it's a little harder to homebrew a tracking generator there.
Try to get ahold of an old HP8620C sweep generator (and plug-ins) and use the HP8569B's "MAX HOLD" setting when sweeping the device to test.