You can't.  If your PA resident client and the NR spouse elect to file the PA return jointly, the NR spouse would be treated as a tax resident for the same period.  You are supposed to be able to file MFS for PA but Lacerte/PTO does not seem to provide a different filing status for PA (although it does for some other states).  This article seems to imply that there is a way but the link is, unfortunately, not working: https://proconnect.intuit.com/community/individual/help/individual-pennsylvania-miscellaneous-inform...

@IntuitAustin @IntuitBettyJo Could you please update the link of this article?  Thanks!