Given that SpecAns are little more than specifically designed receivers, I would argue that SpecAns also are always in a "listen mode." The big requirement would be "GET THE MODEL WITH THE TRACKING GEN."
I'm unfamiliar with the SDR the OP is thinking about, but with the DSA w/TG the OP can design up an LNA for the band of interest, hook it up and use the Tracking Gen to tune it and get it right. Once that's done, plug an antenna into the thing, drive the SpecAn input with the LNA's output, and get a complete idea of what's going on in the spectrum of interest.
The OP would like to listen in, at that point? Build up a down-converter, build up an amplifier for the tracking gen, and then zero-span the spec an for the LO of interest. Poof, the Spec-An provides a decent-enough LO to drive the down-converter and the baseband can be processed further. One could build a simple set of demod radios for a specific IF, and the rest comes out in the wash (all of which can be assisted with by the SpecAn).