I don't really see how it would be possible, as Society bishops do not possess ordinary jurisdiction, and if I'm understanding correctly, a bishop with such jurisdiction is needed to dispense from the impediment of disparity of cult.
I would think that, as a practical matter, the prospective non-Catholic spouse would have to convert. Another possibility would be to apply to the local diocese for such a dispensation (they hand them out more or less as a rubber stamp), which if the SSPX chapel is following the protocols set forth by Rome, would be in keeping with getting permission from the diocese to have an SSPX marriage in the first place.