Standard ac noise analysis uses an "adjoint matrix solution" (probably pnoise does also).  This means that the matrix is solved (inverted) once, and then the transfer functions from each noise source to the output is computed by a matrix-vector product, which is much cheaper than inverting the matrix for each source.

(Of course, the "output" could be differential, not just a single node.)

If you want multiple output nodes, then the simulator has to re-solve the matrix.  Hence, it's really a new analysis.  Of course, most simulators allow you to re-use the dc solution for standard noise, and Spectre should allow you to re-use the PSS for pnoise.

The workaround with ADE is to write the analysis statements by hand, and add them as an include file. But even then, the results processing only expects there to be a single pnoise analysis - but you can access the individual runs through the results browser or using OCEAN.

Regards,

Andrew.