I understand that you would like to remove orbital fringes from unwrapped SAR data. This really depends on the nature of the deformations that you are trying to analyze. Orbital phase error can usually be characterized by its long spatial wavelength. If this wavelength is distinct from the deformations, then it should be relatively easy to remove the orbital error using a linear detrending or high-pass filtering scheme. Note that whatever technique you use, there will always be some residual error.
A more complicated approach is to use the orbital phase information to correct the satellite trajectories, which can then be used to eliminate the error.
You may also want to check with the ROI-PAC team to see if they have any further suggestions.