I just did that in ProSeries.  If I were to do it again, I would complete the 8958 using the joint return already filed -- but then start over with two new returns, and just input the numbers from the 8958.  If there are no separate income items, you might be able to just change the name and switch the SSN's on the first one, to do the second one.  Make sure you save under different names.  

I also used $300 for the charitable deduction on both returns, just because i'm waiting for IRS to admit they made a mistake on that one too.