Is there a means to identify/separate multiple out of phase copies of the same frequency?
It is not possible. Let's consider the case of two cosines, with angles $\theta = 2\pi f_0 t + \alpha$ and $\phi = 2\pi f_0 t + \beta$. Then their sum is equal to $$2\cos\left(\frac{\alpha-\beta}{2}\right)\cos\left(2\pi f_0 t + \frac{\alpha+\beta}{2} \right).$$

Note that, if you measure the amplitude and phase of this signal, you can find plausible candidates for $\alpha$ and $\beta$, but in general there will be multiple possible solutions. Note that the signal could also be zero! As you increase the number of original cosines at $f=f_0$, the ambiguity will also increase.

As a final note, the DFT does provide phase information. The GnuRadio tools, however, only plot the magnitude of the DFT, and there the phase information is lost.